查询LTC1747IFW供应商
FEATURES
■
Sample Rate: 80Msps
■
PGA Front End (2.25V
■
71.8dB SNR and 87dB SFDR (PGA = 0)
■
70.2dB SNR and 87dB SFDR (PGA = 1)
■
500MHz Full Power Bandwidth S/H
■
No Missing Codes
■
Single 5V Supply
■
Power Dissipation: 1.45W
■
Two Pin Selectable Reference Values
■
Data Ready Output Clock
■
Pin Compatible 14-Bit 80Msps Device (LTC1750)
■
48-Pin TSSOP Package
or 1.35V
P-P
Input Range)
P-P
U
APPLICATIO S
■
Direct IF Sampling
■
Telecommunications
■
Receivers
■
Cellular Base Stations
■
Spectrum Analysis
■
Communications Test Equipment
■
Undersampling
LTC1749
12-Bit, 80Msps
Wide Bandwidth ADC
U
DESCRIPTIO
The LTC®1749 is an 80Msps, 12-bit A/D converter designed for digitizing wide dynamic range signals up to
frequencies of 500MHz. The input range of the ADC can be
optimized with the on-chip PGA sample-and-hold circuit
and flexible reference circuitry.
The LTC1749 has a highly linear sample-and-hold circuit
with a bandwidth of 500MHz. The SFDR is 80dB with an
input frequency of 250MHz. Ultralow jitter of 0.15ps
allows undersampling of IF frequencies with minimal
degradation in SNR. DC specs include ±1LSB INL and no
missing codes.
The digital interface is compatible with 5V, 3V, 2V and
LVDS logic systems. The ENC and ENC inputs may be
driven differentially from PECL, GTL and other low swing
logic families or from single-ended TTL or CMOS. The low
noise, high gain ENC and ENC inputs may also be driven
by a sinusoidal signal without degrading performance. A
separate output power supply can be operated from 0.5V
to 5V, making it easy to connect directly to low voltage
DSPs or FIFOs.
The 48-pin TSSOP package with a flow-through pinout
simplifies the board layout.
, LTC and LT are registered trademarks of Linear Technology Corporation.
RMS
BLOCK DIAGRA
PGA
+
A
IN
±1.125V
DIFFERENTIAL
ANALOG INPUT
4.7µF
A
SENSE
V
–
IN
RANGE
SELECT
CM
2V
REF
W
80Msps, 12-Bit ADC with a 2.25V Differential Input Range
CORRECTION
LOGIC AND
SHIFT
REGISTER
CONTROL LOGIC
ENC
0.1µF0.1µF
DIFFERENTIAL
ENCODE INPUT
BUFFER
S/H
CIRCUIT
DIFF AMP
1µF1µF
12-BIT
PIPELINED ADC
REFHAREFLB
4.7µF
REFLA REFHB
12
ENC
OUTPUT
LATCHES
MSBINV
OV
DD
0.1µF
D11
•
•
•
D0
CLKOUT
OGND
V
DD
1µF 1µF 1µF
GND
1749 BD
0.5V TO 5V
0.1µF
5V
1749f
1
LTC1749
WW
W
U
ABSOLUTE MAXIMUM RATINGS
OVDD = VDD (Notes 1, 2)
Supply Voltage (VDD)............................................. 5.5V
Analog Input Voltage (Note 3) .... – 0.3V to (VDD + 0.3V)
Digital Input Voltage (Note 4) ..... –0.3V to (VDD + 0.3V)
Digital Output Voltage................. – 0.3V to (VDD + 0.3V)
OGND Voltage..............................................–0.3V to 1V
Power Dissipation............................................ 2000mW
Operating Temperature Range
LTC1749C ............................................... 0°C to 70°C
LTC1749I............................................ – 40°C to 85°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
U
W
U
PACKAGE/ORDER INFORMATION
TOP VIEW
SENSE
V
GND
A
A
GND
V
V
GND
REFLB
REFHA
GND
GND
REFLA
REFHB
GND
V
V
GND
V
GND
MSBINV
ENC
ENC
1
2
CM
3
+
4
IN
–
5
IN
6
7
DD
8
DD
9
10
11
12
13
14
15
16
17
DD
18
DD
19
20
DD
21
22
23
24
FW PACKAGE
48-LEAD PLASTIC TSSOP
T
= 150°C, θJA = 35°C/W
JMAX
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
OF
OGND
D11
D10
D9
OV
DD
D8
D7
D6
D5
OGND
GND
GND
D4
D3
D2
OV
DD
D1
D0
NC
NC
OGND
CLKOUT
PGA
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ORDER PART
NUMBER
LTC1749CFW
LTC1749IFW
U
CO VERTER CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C. (Note 5)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Resolution (No Missing Codes) ● 12 Bits
Integral Linearity Error (Note 6) – 1.0 ±0.4 1.0 LSB
Differential Linearity Error ● –0.8 ±0.2 0.8 LSB
Offset Error (Note 7) External Reference (V
Gain Error External Reference (V
Full-Scale Tempco Internal Reference ±40 ppm/°C
Offset Tempco ±20 µV/°C
Input Referred Noise (Transition Noise) V
External Reference (V
= 1.125V, PGA = 0 0.23 LSB
SENSE
The ● indicates specifications which apply over the full operating
● –1.5 1.5 LSB
= 1.125V, PGA = 0) –35 ±835 mV
SENSE
= 1.125V, PGA = 0) –3.5 ±1 3.5 %FS
SENSE
= 1.125V) ±20 ppm/°C
SENSE
RMS
UU
A ALOG I PUT
specifications are at TA = 25°C. (Note 5)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
IN
I
IN
C
IN
t
ACQ
t
AP
t
JITTER
CMRR Analog Input Common Mode Rejection Ratio 1.5V < (A
Analog Input Range (Note 8) 4.75V ≤ VDD ≤ 5.25V ● ±0.7 to ±1.125 V
Analog Input Leakage Current 0 < A
Analog Input Capacitance Sample Mode ENC < ENC 6.9 pF
Sample-and-Hold Acquisition Time ● 56ns
Sample-and-Hold Acquisition Delay Time 0 ns
Sample-and-Hold Acquisition Delay Time Jitter 0.15 ps
The ● indicates specifications which apply over the full operating temperature range, otherwise
+
–
, A
< V
IN
IN
DD
Hold Mode ENC > ENC 2.4 pF
–
+
= A
IN
) < 3V 80 dB
IN
● –1 1 µA
RMS
1749f
2
LTC1749
UW
DY A IC ACCURACY
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
SNR Signal-to-Noise Ratio 5MHz Input Signal (PGA = 0) 71.8 dB
SFDR Spurious Free Dynamic Range 5MHz Input Signal (PGA = 0) 87 dB
S/(N + D) Signal-to-(Noise + Distortion) Ratio 5MHz Input Signal (PGA = 0) 71.7 dB
THD Total Harmonic Distortion 5MHz Input Signal, First 5 Harmonics (PGA = 0) –87 dB
IMD Intermodulation Distortion f
Sample-and-Hold Bandwidth R
TA = 25°C, AIN = –1dBFS (Note 5), V
5MHz Input Signal (PGA = 1) 70.2 dB
30MHz Input Signal (PGA = 0) 70.5 71.7 dB
30MHz Input Signal (PGA = 1) 70.2 dB
70MHz Input Signal (PGA = 0) 71.4 dB
70MHz Input Signal (PGA = 1) 68.8 70.1 dB
140MHz Input Signal (PGA = 1) 69.8 dB
250MHz Input Signal (PGA = 1) 69.3 dB
350MHz Input Signal (PGA = 1) 67.4 dB
5MHz Input Signal (PGA = 1) 87 dB
30MHz Input Signal (PGA = 0) (HD2 and HD3) 76 87 dB
30MHz Input Signal (PGA = 0) (Other) 83 90 dB
70MHz Input Signal (PGA = 0) 85 dB
70MHz Input Signal (PGA = 1) (HD2 and HD3) 76 87 dB
70MHz Input Signal (PGA = 1) (Other) 83 90 dB
140MHz Input Signal (PGA = 1) 84 dB
250MHz Input Signal (PGA = 1) 80 dB
350MHz Input Signal (PGA = 1) 74 dB
5MHz Input Signal (PGA = 1) 70.1 dB
30MHz Input Signal (PGA = 0) 71.6 dB
30MHz Input Signal (PGA = 1) 70.0 dB
70MHz Input Signal (PGA = 0) 71.2 dB
70MHz Input Signal (PGA = 1) 69.9 dB
250MHz Input Signal (PGA = 1) 68.6 dB
5MHz Input Signal, First 5 Harmonics (PGA = 1) –87 dB
30MHz Input Signal, First 5 Harmonics (PGA = 0) –87 dB
30MHz Input Signal, First 5 Harmonics (PGA = 1) –87 dB
70MHz Input Signal, First 5 Harmonics (PGA = 0) –85 dB
70MHz Input Signal, First 5 Harmonics (PGA = 1) –87 dB
250MHz Input Signal (PGA = 1) 78 dB
= 2.52MHz, f
IN1
= 2.52MHz, f
f
IN1
= 50Ω 500 MHz
SOURCE
= 5.2MHz (PGA = 0) –87 dBc
IN2
= 5.2MHz (PGA = 1) –87 dBc
IN2
SENSE
= V
DD
UU U
I TER AL REFERE CE CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
VCM Output Voltage I
VCM Output Tempco I
VCM Line Regulation 4.75V ≤ VDD ≤ 5.25V 3 mV/V
VCM Output Resistance 1mA ≤ I
= 0 1.95 2 2.05 V
OUT
= 0 ±30 ppm/°C
OUT
≤ 1mA 4 Ω
OUT
(Note 5)
1749f
3
LTC1749
UU
DIGITAL I PUTS A D DIGITAL OUTPUTS
operating temperature range, otherwise specifications are at TA = 25°C. (Note 5)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
IH
V
IL
I
IN
C
IN
V
OH
V
OL
I
SOURCE
I
SINK
High Level Input Voltage VDD = 5.25V, MSBINV and PGA ● 2.4 V
Low Level Input Voltage VDD = 4.75V, MSBINV and PGA ● 0.8 V
Digital Input Current VIN = 0V to V
Digital Input Capacitance MSBINV and PGA Only 1.5 pF
High Level Output Voltage OVDD = 4.75V IO = –10µA 4.74 V
Low Level Output Voltage OVDD = 4.75V IO = 160µA 0.05 V
Output Source Current V
Output Sink Current V
OUT
OUT
DD
= 0V –50 mA
= 5V 50 mA
The ● indicates specifications which apply over the full
● ±10 µA
IO = –200µA ● 4 4.74 V
IO = 1.6mA ● 0.1 0.4 V
WU
POWER REQUIRE E TS
range, otherwise specifications are at TA = 25°C. (Note 5)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
I
DD
P
OV
DD
DIS
DD
Positive Supply Voltage 4.75 5.25 V
Positive Supply Current ● 290 338 mA
Power Dissipation ● 1.45 1.69 W
Digital Output Supply Voltage 0.5 V
The ● indicates specifications which apply over the full operating temperature
DD
V
UW
TI I G CHARACTERISTICS
range, otherwise specifications are at TA = 25°C. (Note 5)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
t
0
t
1
t
2
t
3
t
4
t
5
t
6
t
7
t
8
t
9
t
10
ENC Period (Note 9) ● 12.5 2000 ns
ENC High (Note 8) ● 6 1000 ns
ENC Low (Note 8) ● 6 1000 ns
Aperture Delay (Note 8) 0 ns
ENC to CLKOUT Falling CL = 10pF (Note 8) ● 1 2.4 4 ns
ENC to CLKOUT Rising CL = 10pF (Note 8) t1 + t
For 80Msps 50% Duty Cycle CL = 10pF (Note 8) ● 7.25 8.65 10.25 ns
ENC to DATA Delay CL = 10pF (Note 8) ● 2 4.9 7.2 ns
ENC to DATA Delay (Hold Time) (Note 8) ● 1.4 3.4 4.7 ns
ENC to DATA Delay (Setup Time) CL = 10pF (Note 8) t0 – t
For 80Msps 50% Duty Cycle CL = 10pF (Note 8) ● 5.3 7.6 10.5 ns
CLKOUT to DATA Delay (Hold Time), (Note 8) ● 6ns
80Msps 50% Duty Cycle
CLKOUT to DATA Delay (Setup Time), CL = 10pF (Note 8) ● 2.1 ns
80Msps 50% Duty Cycle
Data Latency 5 cycles
The ● indicates specifications which apply over the full operating temperature
4
6
ns
ns
4
1749f
ELECTRICAL CHARACTERISTICS
LTC1749
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: All voltage values are with respect to GND (unless otherwise
noted).
Note 3: When these pin voltages are taken below GND or above V
DD
, they
will be clamped by internal diodes. This product can handle input currents
of greater than 100mA below GND or above V
without latchup.
DD
Note 4: When these pin voltages are taken below GND, they will be
clamped by internal diodes. This product can handle input currents of
>100mA below GND without latchup. These pins are not clamped to VDD.
Note 5: V
DD
= 5V, f
sine wave, input range = ±1.125V differential, unless otherwise specified.
Note 6: Integral nonlinearity is defined as the deviation of a code from a
straight line passing through the actual endpoints of the transfer curve.
The deviation is measured from the center of the quantization band.
Note 7: Bipolar offset is the offset voltage measured from –0.5 LSB
when the output code flickers between 0000 0000 0000 and
1111 1111 1111.
Note 8: Guaranteed by design, not subject to test.
Note 9: Recommended operating conditions.
UW
TYPICAL PERFOR A CE CHARACTERISTICS
INL
1.0
0.8
0.6
0.4
0.2
0
–0.2
ERROR (LSB)
–0.4
–0.6
–0.8
–1.0
0
1024
2048
OUTPUT CODE
3072
4096
1749 G01
DNL
1.0
0.8
0.6
0.4
0.2
0
–0.2
ERROR (LSB)
–0.4
–0.6
–0.8
–1.0
0
1024
2048
OUTPUT CODE
3072
1749 G02
= 80MHz, differential ENC/ENC = 2V
SAMPLE
8192 Point FFT, fIN = 15MHz,
–1dB, PGA = 0
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
4096
–120
5
0
10
20
15
FREQUENCY (MHz)
25
P-P
30
80MHz
35
1749 G03
40
8192 Point FFT, fIN = 15MHz,
–10dB, PGA = 0
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
5
0
10
20
15
FREQUENCY (MHz)
8192 Point FFT, fIN = 15MHz,
–20dB, PGA = 0
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
25
30
35
1749 G04
40
–120
20
5
0
10
15
FREQUENCY (MHz)
25
30
35
1749 G05
40
8192 Point FFT, fIN = 30.2MHz,
–1dB, PGA = 0
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
5
0
10
20
15
FREQUENCY (MHz)
25
30
35
1749 G06
40
1749f
5
LTC1749
UW
TYPICAL PERFOR A CE CHARACTERISTICS
8192 Point FFT, fIN = 30.2MHz,
–10dB, PGA = 0
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
5
0
10
20
15
FREQUENCY (MHz)
25
8192 Point FFT, fIN = 70.03MHz,
–10dB, PGA = 0
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
5
0
10
20
15
FREQUENCY (MHz)
25
8192 Point FFT, fIN = 30.2MHz,
–20dB, PGA = 0
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
35
1749 G07
40
30
–120
5
0
10
20
15
FREQUENCY (MHz)
25
35
1749 G08
40
30
8192 Point FFT, fIN = 70.03MHz,
–20dB, PGA = 0
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
35
1749 G10
40
30
–120
5
0
10
20
15
FREQUENCY (MHz)
25
35
1749 G11
40
30
8192 Point FFT, fIN = 70.03MHz,
–1dB, PGA = 0
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
5
0
10
20
15
FREQUENCY (MHz)
25
8192 Point FFT, fIN = 140.2MHz,
–1dB, PGA = 1
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
5
0
10
20
15
FREQUENCY (MHz)
25
35
1749 G09
35
1749 G12
40
40
30
30
8192 Point FFT, fIN = 140.2MHz,
–10dB, PGA = 1
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
5
0
10
20
15
FREQUENCY (MHz)
6
8192 Point FFT, fIN = 140.2MHz,
–20dB, PGA = 1
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
25
30
35
1749 G13
40
–120
20
5
0
10
15
FREQUENCY (MHz)
25
30
35
1749 G14
40
8192 Point FFT, fIN = 250.2MHz,
–1dB, PGA = 1
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
5
0
10
20
15
FREQUENCY (MHz)
25
35
1749 G15
40
1749f
30
UW
INPUT LEVEL (dBFS)
–80
0
SFDR (dBc AND dBFS)
20
40
60
80
–70 –60 –50 –40
1749G21
–30 0
100
10
30
50
70
90
110
–20 –10
TYPICAL PERFOR A CE CHARACTERISTICS
LTC1749
8192 Point FFT, fIN = 250.2MHz,
–10dB, PGA = 1
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
5
0
10
20
15
FREQUENCY (MHz)
25
8192 Point 2-Tone FFT, 65.01MHz
and 70.01MHz, –7dB, PGA = 0
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
5
0
10
20
15
FREQUENCY (MHz)
25
8192 Point FFT, fIN = 250.2MHz,
–20dB, PGA = 1
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
35
1749 G16
40
30
–120
5
0
10
20
15
FREQUENCY (MHz)
25
35
1749 G17
40
30
SFDR vs 30.2MHz Input Level,
PGA = 0
110
100
90
80
70
60
50
40
SFDR (dBc AND dBFS)
30
20
10
0
–70 –60 –50 –40
35
1749 G19
40
30
–80
INPUT LEVEL (dBFS)
–20 –10
–30 0
1749 G20
8192 Point 2-Tone FFT, 25.01MHz
and 30.1MHz, –7dB, PGA = 0
0
–10
–20
–30
–40
–50
–60
–70
–80
AMPLITUDE (dBFS)
–90
–100
–110
–120
5
0
10
20
15
FREQUENCY (MHz)
25
SFDR vs 70.2MHz, Input Level,
PGA = 0
35
1749 G18
40
30
120
100
80
60
40
SFDR (dBc AND dBFS)
20
SFDR vs 140.2MHz, Input Level,
PGA = 1
0
–80
–60 –40
–70 –50
INPUT LEVEL (dBFS)
–30
–20
–10
1749 G22
SNR vs Input Frequency and
SFDR vs 250.2MHz, Input Level
120
100
80
60
40
SFDR (dBc AND dBFS)
20
0
0
–80
–60 –40
–70 –50
INPUT LEVEL (dBFS)
–30
–20
–10
0
1749 G23
Amplitude, PGA = 0
72.0
71.5
71.0
70.5
70.0
SNR (dBFS)
69.5
69.0
68.5
68.0
50 100 200
0
INPUT FREQUENCY (MHz)
–1dB
150
–10dB
250
–20dB
300
1749 G24
1749f
7
LTC1749
SAMPLE RATE (Msps)
0
290
300
310
80
1749 G30
280
270
20 40 60 100
260
250
240
SUPPLY CURRENT (mA)
UW
TYPICAL PERFOR A CE CHARACTERISTICS
SNR vs Input Frequency and
Amplitude, PGA = 1
71.0
70.5
70.0
69.5
69.0
68.5
68.0
SNR (dBFS)
67.5
67.0
66.5
66.0
0
100
200
INPUT FREQUENCY (MHz)
–20dB
–10dB
–1dB
300
SFDR and SNR vs Sample Rate,
15.2MHz, –1dB Input
100
95
90
85
80
75
SFDR AND SNR (dBFS)
70
65
60
20 40 80
0
SAMPLE RATE (Msps)
SFDR
SNR
60
400
100
1749 G25
1749 G28
500
120
SFDR (HD2 and HD3) vs Input
Frequency and Amplitude,
PGA = 0
100
90
80
SFDR (dBFS)
70
60
0
50 100 150 200
INPUT FREQUENCY (MHz)
–10dB
–20dB
–1dB
SFDR and SNR vs VDD, 15.2MHz,
–1dB Input
100
95
90
85
80
75
SFDR AND SNR (dBFS)
70
65
60
4.3 4.5 4.9
4.1
SFDR
SNR
4.7
VDD (V)
250 300
1749 G26
5.1 5.3 5.5
1749 G29
SFDR (HD2 and HD3) vs Input
Frequency and Amplitude,
PGA = 1
100
90
–1dB
80
70
SFDR (dBFS)
60
50
100
0
INPUT FREQUENCY (MHz)
200
300
Supply Current vs Sample Rate
–10dB
400
–20dB
500
1749 G27
8
1749f
LTC1749
U
UU
PI FU CTIO S
SENSE (Pin 1): Reference Sense Pin. GND selects a V
of 0.7V. VDD selects 1.125V. When V
and 1.125V, V
is ±V
VCM (Pin 2): 2.0V Output and Input Common Mode Bias.
Bypass to ground with 4.7µF ceramic chip capacitor.
GND (Pins 3, 6, 9, 12, 13, 16, 19, 21, 36, 37): ADC Power
Ground.
A
IN
A
IN
VDD (Pins 7, 8, 17, 18, 20): 5V Supply. Bypass to AGND
with 1µF ceramic chip capacitors at Pin 8 and Pin 18.
REFLB (Pin 10): ADC Low Reference. Bypass to Pin 11
with 0.1µF ceramic chip capacitor. Do not connect to
Pin␣ 14.
REFHA (Pin 11): ADC High Reference. Bypass to Pin 10 with
0.1µF ceramic chip capacitor, to Pin 14 with a 4.7µF ceramic
capacitor and to ground with 1µF ceramic capacitor.
REFLA (Pin 14): ADC Low Reference. Bypass to Pin 15 with
0.1µF ceramic chip capacitor, to Pin 11 with a 4.7µF ce-
ramic capacitor and to ground with 1µF ceramic capacitor.
REFHB (Pin 15): ADC High Reference. Bypass to Pin 14
with 0.1µF ceramic chip capacitor. Do not connect to
Pin␣ 11.
/PGA gain.
REF
+
(Pin 4): Positive Differential Analog Input.
–
(Pin 5): Negative Differential Analog Input.
is used as V
SENSE
REF
is between 0.7V
SENSE
. The ADC input range
REF
MSBINV (Pin 22): MSB Inversion Control. Low inverts the
MSB, 2’s complement output format. High does not invert
the MSB, offset binary output format.
ENC (Pin 23): Encode Input. The input sample starts on the
positive edge.
ENC (Pin 24): Encode Complement Input. Conversion
starts on the negative edge. Bypass to ground with 0.1µF
ceramic for single-ended ENCODE signal.
PGA (Pin 25): Programmable Gain Amplifier Control. Low
selects an effective front-end gain of 1. High selects an
effective gain of 1 2/3. The ADC input range is ±V
gain.
CLKOUT (Pin 26): Data Valid Output. Latch data on the
rising edge of CLKOUT.
OGND (Pins 27, 38, 47): Output Driver Ground.
NC (Pins 28, 29): No Internal Connection.
D0, D1 (Pins 30, 31): Digital Outputs.
OVDD (Pins 32, 43): Positive Supply for the Output Driv-
ers. Bypass to ground with 0.1µF ceramic chip capacitor.
D2-D4 (Pins 33 to 35): Digital Outputs.
D5-D8 (Pins 39 to 42): Digital Outputs.
D9-D11 (Pins 44 to 46): Digital Outputs.
OF (Pin 48): Over/Under Flow Output. High when an over
or under flow has occurred.
REF
/PGA
1749f
9
LTC1749
UWW
TI I G DIAGRA
N
ANALOG
INPUT
•
t
3
t
2
t
8
DATA (N – 5)
DB11 TO DB0
ENC
DATA
CLKOUT
t
1
t
7
t
6
t
4
t
5
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APPLICATIO S I FOR ATIO
DYNAMIC PERFORMANCE
Signal-to-Noise Plus Distortion Ratio
The signal-to-noise plus distortion ratio [S/(N + D)] is the
ratio between the RMS amplitude of the fundamental input
frequency and the RMS amplitude of all other frequency
components at the ADC output. The output is band limited
to frequencies above DC to below half the sampling
frequency.
Signal-to-Noise Ratio
The signal-to-noise ratio (SNR) is the ratio between the
RMS amplitude of the fundamental input frequency and
the RMS amplitude of all other frequency components
except the first five harmonics and DC.
Total Harmonic Distortion
Total harmonic distortion is the ratio of the RMS sum of all
harmonics of the input signal to the fundamental itself. The
out-of-band harmonics alias into the frequency band
between DC and half the sampling frequency. THD is
expressed as:
t
0
DATA (N – 4)
DB11 TO DB0
t
10
t
9
DATA (N – 3)
1749 TD
where V1 is the RMS amplitude of the fundamental frequency and V2 through Vn are the amplitudes of the
second through nth harmonics. The THD calculated in this
data sheet uses all the harmonics up to the fifth.
Intermodulation Distortion
If the ADC input signal consists of more than one spectral
component, the ADC transfer function nonlinearity can
produce intermodulation distortion (IMD) in addition to
THD. IMD is the change in one sinusoidal input caused by
the presence of another sinusoidal input at a different
frequency.
If two pure sine waves of frequencies fa and fb are applied
to the ADC input, nonlinearities in the ADC transfer function can create distortion products at the sum and difference frequencies of mfa ± nfb, where m and n = 0, 1, 2, 3,
etc. The 3rd order intermodulation products are 2fa + fb,
2fb + fa, 2fa – fb and 2fb – fa. The intermodulation
distortion is defined as the ratio of the RMS value of either
input tone to the RMS value of the largest 3rd order
intermodulation product.
THD Log
=
10
20
222 2
VVV Vn
+++
234
V
1
...
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LTC1749
Spurious Free Dynamic Range (SFDR)
Spurious free dynamic range is the peak harmonic or
spurious noise that is the largest spectral component
excluding the input signal and DC. This value is expressed
in decibels relative to the RMS value of a full scale input
signal.
Input Bandwidth
The input bandwidth is that input frequency at which the
amplitude of the reconstructed fundamental is reduced by
3dB for a full scale input signal.
Aperture Delay Time
The time from when a rising ENC equals the ENC voltage
to the instant that the input signal is held by the sample and
hold circuit.
Aperture Delay Jitter
The variation in the aperture delay time from conversion to
conversion. This random variation will result in noise
when sampling an AC input. The signal to noise ratio due
to the jitter alone will be:
SNR
= –20log (2π) • FIN • T
JITTER
JITTER
CONVERTER OPERATION
The LTC1749 is a CMOS pipelined multistep converter with
a front-end PGA. The converter has four pipelined ADC
stages; a sampled analog input will result in a digitized value
five cycles later, see the Timing Diagram section. The analog
input is differential for improved common mode noise
immunity and to maximize the input range. Additionally,
the differential input drive will reduce even order harmonics of the sample-and-hold circuit. The encode input is also
differential for improved common mode noise immunity.
The LTC1749 has two phases of operation, determined by
the state of the differential ENC/ENC input pins. For brevity, the text will refer to ENC greater than ENC as ENC high
and ENC less than ENC as ENC low.
Each pipelined stage shown in Figure 1 contains an ADC,
a reconstruction DAC and an interstage residue amplifier.
PGA
A
A
V
4.7µF
SENSE
+
IN
INPUT
S/H
–
IN
CM
2.0V
REFERENCE
RANGE
SELECT
REF
BUF
FIRST PIPELINED
ADC STAGE
(5 BITS)
SECOND PIPELINED
DIFF
REF
AMP
0.1µF 0.1µF
4.7µF
1µF
ADC STAGE
(4 BITS)
1µF
INTERNAL CLOCK SIGNALSREFL REFH
DIFFERENTIAL
INPUT
LOW JITTER
CLOCK
DRIVER
ENCREFHAREFLB REFLA REFHB ENC
THIRD PIPELINED
ADC STAGE
(4 BITS)
CONTROL LOGIC
AND
CALIBRATION LOGIC
FOURTH PIPELINED
ADC STAGE
(2 BITS)
SHIFT REGISTER
AND CORRECTION
OUTPUT
DRIVERS
MSBINV OGND
OV
DD
OF
D11
D0
CLKOUT
1749 F01
0.5V TO
5V
Figure 1. Functional Block Diagram
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LTC1749
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APPLICATIO S I FOR ATIO
In operation, the ADC quantizes the input to the stage and
the quantized value is subtracted from the input by the
DAC to produce a residue. The residue is amplified and
output by the residue amplifier. Successive stages operate
out of phase so that when the odd stages are outputting
their residue, the even stages are acquiring that residue
and visa versa.
When ENC is low, the analog input is sampled differentially
directly onto the input sample-and-hold capacitors, inside
the “Input S/H” shown in the block diagram. At the instant
that ENC transitions from low to high, the sampled input
is held. While ENC is high, the held input voltage is
buffered by the S/H amplifier which drives the first pipelined
ADC stage. The first stage acquires the output of the S/H
during this high phase of ENC. When ENC goes back low,
the first stage produces its residue which is acquired by
the second stage. At the same time, the input S/H goes
back to acquiring the analog input. When ENC goes back
high, the second stage produces its residue which is
acquired by the third stage. An identical process is repeated for the third stage, resulting in a third stage residue
that is sent to the fourth stage ADC for final evaluation.
Each ADC stage following the first has additional range to
accommodate flash and amplifier offset errors. Results
from all of the ADC stages are digitally synchronized such
that the results can be properly combined in the correction
logic before being sent to the output buffer.
SAMPLE/HOLD OPERATION AND INPUT DRIVE
Sample/Hold Operation
Figure 2 shows an equivalent circuit for the LTC1749
CMOS differential sample-and-hold. The differential analog inputs are sampled directly onto sampling capacitors
(C
SAMPLE
) through NMOS switches. This direct capacitor
sampling results in lowest possible noise for a given
sampling capacitor size. The capacitors shown attached to
each input (C
PARASITIC
) are the summation of all other
capacitance associated with each input.
During the sample phase when ENC/ENC is low, the NMOS
switch connects the analog inputs to the sampling capacitors and they charge to, and track the differential input
voltage. When ENC/ENC transitions from low to high the
LTC1749
V
A
A
ENC
ENC
DD
+
IN
V
DD
–
IN
2V
6k
6k
2V
C
PARASITIC
2.4pF
C
PARASITIC
2.4pF
5V
Figure 2. Equivalent Input Circuit
BIAS
R
ON
30Ω
R
ON
30Ω
C
PARASITIC
1pF
C
PARASITIC
1pF
C
SAMPLE
3.5pF
C
SAMPLE
3.5pF
1749 F02
sampled input voltage is held on the sampling capacitors.
During the hold phase when ENC/ENC is high the sampling
capacitors are disconnected from the input and the held
voltage is passed to the ADC core for processing. As
ENC/ENC transitions from high to low the inputs are
reconnected to the sampling capacitors to acquire a new
sample. Since the sampling capacitors still hold the previous sample, a charging glitch proportional to the change
in voltage between samples will be seen at this time. If the
change between the last sample and the new sample is
small the charging glitch seen at the input will be small. If
the input change is large, such as the change seen with
input frequencies near Nyquist, then a larger charging
glitch will be seen.
Common Mode Bias
The ADC sample-and-hold circuit requires differential drive
to achieve specified performance. Each input should swing
within the valid input range, around a common mode voltage of 2.0V. The VCM output pin (Pin␣ 2) may be used to provide the common mode bias level. VCM can be tied directly
to the center tap of a transformer to set the DC input level
or as a reference level to an op amp differential driver circuit. The VCM pin must be bypassed to ground close to the
ADC with a 4.7µF or greater capacitor.
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LTC1749
Input Drive Circuits
The LTC1749 requires differential drive for the analog
inputs. A balanced input drive will minimize even order
harmonics that are due to nonlinear behavior of the input
drive circuits and the S/H circuit.
The S/H circuit of the LTC1749 is a switched capacitor
circuit (Figure 2). The input drive circuitry will see a
sampling glitch at the start of the sampling period, when
ENC/ENC falls. Although designed to be linear as possible,
a small fraction of this glitch is nonlinear and can result in
additional observed distortion if the input drive circuitry is
too slow. For most practical circuits the glitch nonlinearity
is more than 100dB below the fundamental. The glitch will
decay during the sampling period with a time constant
determined by the input drive and S/H circuitry.
For fast settling and wide bandwidth, a low drive impedance is required. The S/H bandwidth is partially determined by the source impedance. The full 500MHz
bandwidth is valid for source impedance (each input) less
than 30Ω. Higher source impedance can be used but full
amplitude distortion will be better with a source impedance less than 100Ω.
signal at its optimum DC level of 2V. In this example a 1:1
transformer is used; however, other transformer impedance ratios may be substituted.
Figure 3b shows the use of a transformer without a center
tapped secondary. In this example the secondary is biased
with the addition of two resistors placed in series across
the secondary winding. The center tap of the secondary
resistors is connected to the ADC VCM output to set the DC
bias. This circuit is better suited for high input frequency
applications since center tapped transformers generally
have less bandwidth and poor balance at high frequencies
than noncenter tapped transformers.
V
CM
4.7µF
LTC1749
ANALOG
INPUT
0.1µF
1:1
100Ω 100Ω 12pF
Figure 3a. Single-Ended to Differential
Conversion Using a Transformer
25Ω
25Ω
12pF
12pF
25Ω
25Ω
+
A
IN
–
A
IN
1749 F03
Transformers
Transformers provide a simple method for converting a
single-ended signal to a differential signal; however, they
have poor performance characteristics at low and high input
frequencies. The lower –3dB corner of RF transformers can
range from tens of kHz to tens of MHz. Operation near this
corner results in poor 2nd order harmonic performance
due to nonlinear transformer core behavior. The upper
–3dB corner can vary from tens of MHz to several GHz.
Operation near the upper corner can result in poor 2nd order
performance due to poor balance on the secondary.
Transformers should be selected to have –3dB corners at
least one octave away from the desired operating frequency. Transformers with larger cores usually have
better performance at lower frequency and perform better
when driving heavy loads.
Figure 3a shows the LTC1749 being driven by an RF
transformer with a center tapped secondary. The secondary center tap is DC-biased with VCM, setting the ADC input
V
ANALOG
INPUT
0.1µF
1:4
100Ω
Figure 3b. Using a Transformer
Without a Center Tapped Secondary
10Ω
200Ω
200Ω
10Ω
4.7µF
8.4pF
8.4pF
25Ω
25Ω
CM
LTC1749
+
A
IN
–
A
IN
1749 F03b
Active Drive Circuits
Active circuits, open loop or closed loop, can be used to
drive the ADC inputs. Closed-loop circuits such as op amps
have excellent DC and low frequency accuracy but have
poor high frequency performance. Figure 4 shows the dual
LT®1818 op amp used for single-ended to differential
signal conver
sion. Note that the two op amps do not have
the same noise gain, which can result in poor balance at
higher frequencies. The op amp configured in a gain of +1
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LTC1749
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APPLICATIO S I FOR ATIO
V
CM
12pF
4.7µF
12pF
25Ω
25Ω
12pF
+
A
IN
LTC1749
–
A
IN
1749 F04
5V
SINGLE-ENDED
INPUT
2V ±1/2
RANGE
+
1/2 LT1818
25Ω
–
100Ω
+
1/2 LT1818
25Ω
–
500Ω 500Ω
Figure 4. Differential Drive with Op Amps
can be configured in a noise gain of +2 with the addition of
two equal valued resistors between the output and inverting input and between the two inputs. This however will raise
the noise contributed by the op amps.
Reference Operation
TIE TO V
FOR V
DD
TIE TO GND FOR V
V
REF
0.7V < V
SENSE
LTC1749
4Ω
V
= V
= 1.125;
REF
REF
SENSE
< 1.125V
2V
= 0.7V;
FOR
1µF
1µF
CM
4.7µF
CONTROL
SENSE
REFLB
0.1µF
REFHA
4.7µF
REFLA
0.1µF
REFHB
RANGE
DETECT
AND
2V BANDGAP
REFERENCE
INTERNAL ADC
HIGH REFERENCE
DIFF AMP
INTERNAL ADC
LOW REFERENCE
Figure 5. Equivalent Reference Circuit
1.125V
0.7V
BUFFER
V
REF
1749 F05
Figure 5 shows the LTC1749 equivalent reference circuitry
consisting of a 2V bandgap reference, a 3-to-1 switch, a
switch control circuit and a difference amplifier.
The 2V bandgap reference serves two functions. First, it is
assessable at the VCM pin to provide a DC bias point for
setting the common mode voltage of any external input
circuitry. Second, it is used to derive internal reference
levels that may be used to set the input range of the ADC.
An external bypass capacitor is required for the 2V reference output at the V
pin. This provides a high frequency
CM
low impedance path to ground for internal and external
circuitry. This is also the compensation capacitor for the
reference, which will not be stable without this capacitor.
To achieve the optimal input range for an application, the
internal reference voltage (V
switch shown in Figure 5 connects V
) is flexible. The reference
REF
to one of two
REF
internally derived reference voltages, or to an externally
derived reference voltage. The internally derived references are selected by strapping the SENSE pin to GND for
0.7V, or to VDD for 1.125V. When 0.7V > V
SENSE
> 1.125V,
V
is directly connected to V
SENSE
. Because of the dual
REF
nature of the SENSE pin, driving it with a logic device is not
recommended.
Reference voltages between 0.7V and 1.125V may be
programmed with two external resistors as shown in
Figure 6a. An external reference may be used by applying
its output directly or through a resistor divider to the
SENSE pin (Figure 6b). When the SENSE pin is driven with
an externally derived reference voltage, it should be bypassed to ground as close to the device as possible with
a 1µF ceramic capacitor.
A difference amplifier generates the high and low references for the ADC. High speed switching circuits are
connected to these outputs and they must be externally
bypassed. Each output has two pins: REFHA and REFHB
for the high reference and REFLA and REFLB for the low
reference. The doubled output pins are needed to reduce
package inductance. Bypass capacitors must be connected as shown in Figure 5.
14
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LTC1749
2V
10k
1V
10k
V
CM
4.7µF
SENSE
1µF
LTC1749
1749 F06a
Figure 6a. 2V Range ADC
V
4.7µF
SENSE
CM
LTC1749
1749 F06b
2V
2.5k
1, 2
64
1µF 1µF10k0.1µF
5V
LT1790-1.25
Figure 6b. 2V Range ADC with External Reference
Input Range
The LTC1749 performance may be optimized by adjusting
the ADC’s input range to meet the requirements of the
application. For lower input frequency applications
(< 40MHz), the highest input range of ±1.125V (2.25V) will
provide the best SNR while maintaining excellent SFDR.
For higher input frequencies (>80MHz), a lower input
range will provide better SFDR performance with a reduction in SNR.
The input range of the ADC is determined as ±V
where V
Reference Operation section) and A
is the reference voltage (described in the
REF
is the effective
PGA
REF/APGA
,
PGA gain. Table 1 shows the input range of the ADC versus
the state of the two pins, PGA and SENSE.
Driving the Encode Inputs
The noise performance of the LTC1749 can depend on the
encode signal quality as much as on the analog input. The
ENC/ENC inputs are intended to be driven differentially,
primarily for immunity from common mode noise sources.
Each input is biased through a 6k resistor to a 2V bias. The
bias resistors set the DC operating point for transformer
coupled drive circuits and can set the logic threshold for
single-ended drive circuits.
Any noise present on the encode signal will result in
additional aperture jitter that will be RMS summed with the
inherent ADC aperture jitter.
In applications where jitter is critical (high input frequencies) take the following into consideration:
1. Differential drive should be used.
2. Use as large an amplitude as possible; if transformer
coupled use a higher turns ratio to increase the
amplitude.
3. If the ADC is clocked with a sinusoidal signal, filter the
encode signal to reduce wideband noise.
4. Balance the capacitance and series resistance at both
encode inputs so that any coupled noise will appear at
both inputs as common mode noise.
The encode inputs have a common mode range of 1.8V to
VDD. Each input may be driven from ground to VDD for
single-ended drive.
Table 1
PGA V
0= V
1= V
0 = GND 1.4V
1 = GND 0.84V
0 0.7V < V
1 0.7V < V
SENSE
DD
DD
< 1.125V 2 × V
SENSE
< 1.125V 1.2 × V
SENSE
INPUT RANGE COMMENTS
2.25V
Differential Best Noise, SNR = 71.8dB. Good SFDR, >80dB Up to 100MHz
P-P
1.35V
Differential Improved High Frequency Distortion. SNR = 70.5dB. SFDR > 80dB Up to 250MHz
P-P
Differential Reduced Internal Reference Mode with PGA = 0. Provides Similar Input Range as
P-P
Differential Smallest Possible Input Span. Useful for Improved Distortion at Very High
P-P
Differential Adjustable Input Range with Better Noise Performance. SNR = 71.8dB with
SENSE
Differential Adjustable Input Range with Better High Frequency Distortion. SNR = 70.5dB with
SENSE
V
= VDD and PGA = 0 But with Worse Noise. SNR = 70.3dB
SENSE
Frequencies, But with Reduced Noise Performance. SNR = 69dB
= 1.125V, SNR = 70.3dB with V
V
SENSE
V
= 1.125V, SNR = 69dB with V
SENSE
SENSE
SENSE
= 0.7V
= 0.7V
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V
THRESHOLD
CLOCK
INPUT
= 2V
ANALOG INPUT
0.1µF
50Ω
0.1µF
ENC
ENC2V
1:4
ENC
ENC
LTC1749
V
DD
V
DD
2V BIAS
2V BIAS
5V
6k
6k
Figure 7. Transformer Driven ENC/ENC
LTC1749
1749 F08a
BIAS
MC100LVELT22
D0
3.3V
TO INTERNAL
ADC CIRCUITS
130Ω
Q0
Q0
3.3V
1749 F07
130Ω
83Ω83Ω
ENC
ENC
LTC1749
1749 F08b
Figure 8a. Single-Ended ENC Drive,
Not Recommended for Low Jitter
Maximum and Minimum Encode Rates
The maximum encode rate for the LTC1749 is 80Msps. For
the ADC to operate properly the encode signal should have
a 50% (±4%) duty cycle. Each half cycle must have at least
6ns for the ADC internal circuitry to have enough settling
time for proper operation. Achieving a precise 50% duty
cycle is easy with differential sinusoidal drive using a
transformer or using symmetric differential logic such as
PECL or LVDS. When using a single-ended encode signal
asymmetric rise and fall times can result in duty cycles that
are far from 50%.
At sample rates slower than 80Msps the duty cycle can
vary from 50% as long as each half cycle is at least 6ns.
The lower limit of the LTC1749 sample rate is determined
by droop of the sample-and-hold circuits. The pipelined
Figure 8b. ENC Drive Using a CMOS-to-PECL Translator
architecture of this ADC relies on storing analog signals on
small valued capacitors. Junction leakage will discharge
the capacitors. The specified minimum operating frequency for the LTC1749 is 1Msps.
DIGITAL OUTPUTS
Digital Output Buffers
Figure 9 shows an equivalent circuit for a single output
buffer. Each buffer is powered by OVDD and OGND, isolated from the ADC power and ground. The additional
N-channel transistor in the output driver allows operation
down to low voltages. The internal resistor in series with
the output makes the output appear as 50Ω to external
circuitry and may eliminate the need for external damping
resistors.
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LTC1749
DATA
FROM
LATCH
V
DD
PREDRIVER
LOGIC
Figure 9. Equivalent Circuit for a Digital Output Buffer
V
Output Loading
As with all high speed/high resolution converters the
digital output loading can affect the performance. The
digital outputs of the LTC1749 should drive a minimal
capacitive load to avoid possible interaction between the
digital outputs and sensitive input circuitry. The output
should be buffered with a device such as an ALVCH16373
CMOS latch. For full speed operation the capacitive load
should be kept under 10pF. A resistor in series with the
output may be used but is not required since the ADC has
a series resistor of 43Ω on chip.
Lower OVDD voltages will also help reduce interference
from the digital outputs.
LTC1749
DD
OV
DD
43Ω
1749 F09
OV
DD
OGND
0.5V TO
V
DD
0.1µF
TYPICAL
DATA
OUTPUT
This is necessary when using a sinusoidal encode. Data
will be updated just after CLKOUT falls and can be latched
on the rising edge of CLKOUT.
Output Driver Power
Separate output power and ground pins allow the output
drivers to be isolated from the analog circuitry. The power
supply for the digital output buffers, OVDD, should be tied
to the same power supply as for the logic being driven. For
example if the converter is driving a DSP powered by a 3V
supply then OVDD should be tied to that same 3V supply.
OVDD can be powered with any voltage up to 5V. The logic
outputs will swing between OGND and OVDD.
Format
The LTC1749 parallel digital output can be selected for
offset binary or 2’s complement format. The format is
selected with the MSBINV pin; high selects offset binary.
Overflow Bit
An overflow output bit indicates when the converter is
overranged or underranged. When OF outputs a logic high
the converter is either overranged or underranged.
Output Clock
The ADC has a delayed version of the ENC input available
as a digital output, CLKOUT. The CLKOUT pin can be used
to synchronize the converter data to the digital system.
GROUNDING AND BYPASSING
The LTC1749 requires a printed circuit board with a clean
unbroken ground plane. A multilayer board with an internal ground plane is recommended. The pinout of the
LTC1749 has been optimized for a flowthrough layout so
that the interaction between inputs and digital outputs is
minimized. Layout for the printed circuit board should
ensure that digital and analog signal lines are separated as
much as possible. In particular, care should be taken not
to run any digital track alongside an analog signal track or
underneath the ADC.
High quality ceramic bypass capacitors should be used at
the V
DD, VCM
, REFHA, REFHB, REFLA and REFLB pins as
shown in the block diagram on the front page of this data
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sheet. Bypass capacitors must be located as close to the
pins as possible. Of particular importance are the capacitors between REFHA and REFLB and between REFHB and
REFLA. These capacitors should be as close to the device
as possible (1.5mm or less). Size 0402 ceramic capacitors
are recomended. The large 4.7µF capacitor between REFHA
and REFLA can be somewhat further away. The traces
connecting the pins and bypass capacitors must be kept
short and should be made as wide as possible.
The LTC1749 differential inputs should run parallel and
close to each other. The input traces should be as short as
possible to minimize capacitance and to minimize noise
pickup.
An analog ground plane separate from the digital processing system ground should be used. All ADC ground pins
labeled GND should connect to this plane. All ADC V
bypass capacitors, reference bypass capacitors and input
filter capacitors should connect to this analog plane. The
LTC1749 has three output driver ground pins, labeled
OGND (Pins 27, 38 and 47). These grounds should connect to the digital processing system ground. The output
DD
driver supply, OVDD should be connected to the digital
processing system supply. OVDD bypass capacitors should
bypass to the digital system ground. The digital processing system ground should be connected to the analog
plane at ADC OGND (Pin 38).
HEAT TRANSFER
Most of the heat generated by the LTC1749 is transferred
from the die through the package leads onto the printed
circuit board. In particular, ground pins 12, 13, 36 and 37
are fused to the die attach pad. These pins have the lowest
thermal resistance between the die and the outside environment. It is critical that all ground pins are connected to
a ground plane of sufficient area. The layout of the evaluation circuit shown on the following pages has a low thermal resistance path to the internal ground plane by using
multiple vias near the ground pins. A ground plane of this
size results in a thermal resistance from the die to ambient
of 35°C/W. Smaller area ground planes or poorly connected
ground pins will result in higher thermal resistance.
18
1749f
PACKAGE DESCRIPTIO
0.95 ±0.10
LTC1749
U
FW Package
48-Lead Plastic TSSOP (6.1mm)
(Reference LTC DWG # 05-08-1651)
12.4 – 12.6*
(.488 – .496)
48 46 4544434241 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 2547
8.1 ±0.10
0.32 ±0.05 0.50 TYP
RECOMMENDED SOLDER PAD LAYOUT
6.0 – 6.2**
(.236 – .244)
0.09 – 0.20
(.0035 – .008)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN
3. DRAWING NOT TO SCALE
0.45 – 0.75
(.018 – .029)
MILLIMETERS
(INCHES)
6.2 ±0.10
1345678 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
2
(.0473)
° – 8°
0
-C-
0.50
(.0197)
BSC
*
DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDE
**
DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE
0.17 – 0.27
(.0067 – .0106)
0.05 – 0.15
(.002 – .006)
7.9 – 8.3
(.311 – .327)
1.20
MAX
FW48 TSSOP 0502
-TC.10
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1749f
19
LTC1749
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PART NUMBER DESCRIPTION COMMENTS
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LTC1742 14-Bit, 65Msps ADC Pin Compatible with the LTC1744, LTC1746, LTC1748
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LTC1744 14-Bit, 50Msps ADC Pin Compatible with the LTC1742, LTC1746, LTC1748
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LTC1746 14-Bit, 25Msps ADC Pin Compatible with the LTC1742, LTC1744, LTC1748
LTC1747 12-Bit, 80Msps ADC Pin Compatible with the LTC1741, LTC1743, LTC1745
LTC1748 14-Bit, 80Msps ADC Pin Compatible with the LTC1742, LTC1744, LTC1746
LTC1750 14-Bit, 80Msps ADC with Wide Bandwidth Pin Compatible with the LTC1749
LT1807 325MHz, Low Distortion Dual Op Amp Rail-to-Rail Input and Output
LT5512 High Signal Level Down Converting Mixer DC to 3GHz, 17dBm IIP3, Integrated LO Buffer
LT5515 Direct Conversion Demodulator 1.5GHz to 2.5GHz, 21.5dBm IIP3, Integrated LO Quadrature Generator
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LT5522 High Signal Level Down Converting Mixer 600MHz to 3GHz, 25dBm IIP3, Integrated LO Buffer
20
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
1749f
LT/TP 0204 1K • PRINTED IN THE USA
LINEAR TECHNOLOGY CORPORATION 2004
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