ADC14161
Low-Distortion, Self-Calibrating 14-Bit, 2.5 MSPS,
390 mW A/D Converter
ADC14161 Low-Distortion, Self-Calibrating 14-Bit, 2.5 MSPS, 390 mW A/D Converter
January 2000
General Description
The ADC14161 is a self-calibrating 14-bit, 2.5 Megasample
per secondanalog to digital converter. It operates on a single
+5V supply, consuming just 390mW (typical).
The ADC14161 provides an easy and affordable upgrade
from 12 bit converters. The ADC14161 may also be used to
replace many hybrid converters with a resultant saving of
space, power and cost.
The ADC14161 operates with input frequencies up to
clock frequency. The calibration feature of the ADC14161
can be used to get more consistent and repeatable results
over the entire operating temperature range. On-command
self-calibration reduces many of the effects of
temperature-induced drift, resulting in more repeatable conversions.
Tested and guaranteed dynamic performance specifications
provide the designer with known performance.
The Power Down feature reduces power consumption to
less than 2mW.
TheADC14161 comes in aTQFP and is designed to operate
over the industrial temperature range of −40˚C to +85˚C.
1
⁄2the
Connection Diagram
Features
n Single +5V Operation
n Auto-Calibration
n Power Down Mode
n TTL/CMOS Input/Output compatible
Key Specifications
n Resolution 14 Bits
n Conversion Rate 2.5 Msps (min)
n DNL 0.3 LSB (typ)
n SNR (f
n ENOB 12.8 Bits (typ)
n Supply Voltage +5V
n Power Consumption 390mW (typ)
= 500 kHz) 80 dB (typ)
IN
±
Applications
n Instrumentation
n PC-Based Data Acquisition
n Data Communications
n Blood Analyzers
n Sonar/Radar
%
5
DS100154-1
Ordering Information
Industrial
(−40˚C ≤ TA ≤ +85˚C)
ADC14161CIVT VEG52A 52 Pin Thin Quad Flat Pack
© 2000 National Semiconductor Corporation DS100154 www.national.com
Package
Block Diagram
ADC14161
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DS100154-2
Pin Descriptions and Equivalent Circuits
ADC14161
Pin
Symbol Equivalent Circuit
No.
Analog I/O
1V
4V
48 V
47 V
50 V
49
+
IN
−
IN
REF+IN
REF−IN
REF+OUT
REF−OUT
Description
Non-Inverting analog signal Input. With a 2.0V reference voltage and a
2.0V common mode voltage, V
, the input signal voltage range is from
CM
1.0 volt to 3.0 Volts.
Inverting analog signal Input. With a 2.0V reference voltage and a 2.0V
common mode voltage, VCM, the input signal voltage range is from 1.0 Volt
to 3.0 Volts. The input signal should be balanced for best performance.
Positive reference input. This pin should be bypassed to AGND with a 0.1
µF monolithic capacitor. V
+ minus V
REF
should be a minimum of
REF− IN
1.8V and a maximum of 2.2V. The full-scale input voltage is equal to
V
REF+IN
minus V
REF−IN
.
Negative reference input. In most applications this pin should be connected
to AGND and the full reference voltage applied to V
application requires that V
be offset from AGND, this pin should be
REF−IN
bypassed to AGND with a 0.1 µF monolithic capacitor. V
V
full-scale input voltage is equal to V
should be a minimum of 1.8V and a maximum of 2.2V. The
REF− IN
REF+IN
minus V
REF+IN
REF+IN
REF−IN
.Ifthe
minus
.
Output of the high impedance positive reference buffer. With a 2.0V
reference input, and with a V
of 2.0V, this pin will have a 3.0V output
CM
voltage. This pin should be bypassed to AGND with a 0.1 µF monolithic
capacitor in parallel with a 10 µF capacitor.
The output of the negative reference buffer. With a 2.0V reference and a
of 2.0V, this pin will have a 1.0V output voltage. This pin should be
V
CM
bypassed to AGND with a 0.1 µF monolithic capacitor in parallel with a 10
µF capacitor.
52 V
51 V
Digital I/O
10 Clock
REF (MID)
CM
Output of the reference mid-point, nominally equal to 0.4 VA(2.0V). This
pin should be bypassed to AGND with a 0.1 µF monolithic capacitor. This
voltage is derived from V
CM
.
Input to the common mode buffer, nominally equal to 40%of the supply
voltage (2.0V). This pin should be bypassed to AGND with a 0.1 µF
monolithic capacitor. Best performance is obtained if this pin is driven with
a low impedance source of 2.0V.
Digital clock input. The input voltage is captured tADafter the fall of the
clock signal. The range of frequencies for this input is 300 kHz to 2.5 MHz.
The clock frequency should not be changed or interrupted during
conversion or while reading data output.
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Pin Descriptions and Equivalent Circuits (Continued)
ADC14161
11 CAL
40 RESET
18 RD
44 PD
17 EOC
CAL is a level-sensitive digital input that, when pulsed high for at least two
clock cycles, puts the ADC into the CALIBRATE mode. Calibration should
be performed upon ADC power-up (after asserting a reset) and each time
the temperature changes by more than 50˚C since the ADC14161 was last
calibrated. See Section 2.3 for more information.
RESET is a level-sensitive digital input that, when pulsed high for at least 2
CLOCK cycles, results in the resetting of the ADC. This reset pulse must
be applied after ADC power-up, before calibration.
RD is the (READ) digital input that, when low, enables the output data
buffers. When this input pin is high, the output data bus is in a high
impedance state.
PD is the Power Down input that, when low, puts the converter into the
power down mode. When this pin is high, the converter is in the active
mode.
EOC is a digital output that, when low, indicates the availability of new
conversion results at the data output pins.
23-32
35-38
Analog Power
6, 7,
45
5, 8,
46
D00-13
V
A
AGND
Digital data outputs that make up the 14-bit TRI-STATE conversion results.
D00 is the LSB, while D13 is the MSB (SIGN bit) of the two’s complement
output word.
Positive analog supply pins. These pins should be connected to a clean,
quiet +5V source and bypassed to AGND with 0.1 µF monolithic capacitors
in parallel with 10 µF capacitors, both located within 1 cm of these power
pins.
The ground return for the analog supply. AGND and DGND should be
connected together directly beneath the ADC14161 package. See Section
5 (Layout and grounding) for more details).
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Pin Descriptions and Equivalent Circuits (Continued)
Digital Power
Positive digital supply pin. This pin should be connected to the same clean,
20 V
12,13
14,19
41,42
DGND
43
34 V
D
33 DGND I/O
NC
2, 3,
9,15,
16,21
NC
22,39
D
I/O
quiet +5V source of as is V
monolithic capacitor in parallel with a 10µF capacitor, both located within 1
cm of the power pin.
The ground return for the digital supply. AGND and DGND should be
connected together directly beneath the ADC14161 package. See Section
5 (Layout and Grounding) for more details.
Positive digital supply pin for the ADC14161’s output drivers. This pin
should be connected to a +3V to +5V source and bypassed to DGND I/O
with a 0.1 µF monolithic capacitor. If the supply for this pin is different from
the supply used for V
and VD, it should also be bypassed with a 10 µF
A
capacitor. All bypass capacitors should be located within 1 cm of the
supply pin.
The ground return for the digital supply for the ADC14161’s output drivers.
This pin should be connected to the system digital ground, but not be
connected in close proximity to the ADC14161’s DGND or AGND pins. See
Section 5.0 (Layout and Grounding) for more details.
All pins marked NC (no connect) should be left floating. Do not connect the
NC pins to ground, power supplies, or any other potential or signal. These
pins are used for test in the manufacturing process.
and bypassed to DGND with a 0.1 µF
A
ADC14161
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
ADC14161
Distributors for availability and specifications.
Supply Voltage (V
A,VD,VD
Voltage on Any I/O Pin −0.3V to V
Input Current at Any Pin (Note 3)
Package Input Current (Note 3)
Power Dissipation at T
ESD Susceptibility (Note 5)
Human Body Model 1500V
Machine Model 200V
Soldering Temp., Infrared, 10 sec. (Note 6) 300˚C
I/O) 6.5V
=
25˚C (Note 4)
A
+
+0.3V
±
25mA
±
50mA
Storage Temperature −65˚C to +150˚C
Operating Ratings(Notes 1, 2)
Operating Temperature
Range
V
A,VD
V
I/O 2.7V to V
D
V
− IN 1.0V to 3.0V
REF
V
− IN AGND to 1.0V
REF
Digital Inputs −0.05V to V
|V
| ≤100 mV
A−VD
|AGND - DGND | 0V to 100 mV
−40˚C ≤ T
≤ +85˚C
A
+4.75V to +5.25V
+ 0.05V
D
D
Converter Electrical Characteristics
+
=
=
The following specifications apply for AGND=DGND=DGND I/O=0V, V
PD=+5V, V
limits apply for T
REF+ IN
A
=
+2.0V, V
=
T
J
=
REF− IN
=
to T
T
MIN
AGND, f
: all other limits T
MAX
CLK
=
2.5 MHz, C
=
A
=
L
=
T
25˚C(Notes 7, 8, 9)
J
V
50 pF/pin. After Auto-Cal
Symbol Parameter Conditions
Static Converter Characteristics
Resolution with No
Missing Codes
INL Integral Non Linearity
DNL Differential Non Linearity
Full-Scale Error
Zero Offset Error +0.1
Reference and Analog Input Characteristics
V
IN
Input Voltage Range
(V
IN+−VIN−
)
=
V
V
REF
REF+IN−VREF+IN
(CLK
C
IN
Input Capacitance V
=
1.0V + 0.7Vrms
IN
LOW)
(CLK
HIGH)
Reference Voltage
V
REF
Range [( V
(V
REF−IN
)] (Note 14)
REF+IN
)−
Reference Input
Resistance
Dynamic Converter Characteristics
BW Full Power Bandwidth 8 MHz
SNR Signal-to-Noise Ratio f
SINAD
Signal-to-Noise &
Distortion
ENOB Effective Number of Bits f
THD
SFDR
IMD
Total Harmonic
Distortion
Spurious Free Dynamic
Range
Intermodulation
Distortion
=
IN
=
f
IN
=
IN
=
f
IN
=
f
IN
f
IN1
f
IN2
500 kHz, V
500 kHz, V
500 kHz, V
500 kHz, V
500 kHz, V
=
95 kHz
=
105 kHz
=
1.9V
IN
IN
IN
IN
IN
=
=
=
=
1.9V
1.9V
1.9V
1.9V
P-P
P-P
P-P
P-P
P-P
A
=
V
+5.0V, V
D
Typical
(Note 10)
I/O=3.0V or 5.0V,
D
@
Temperature. Boldface
Limits
(Note 11)
14 Bits(min)
±
±
±
0.75
0.3
0.4
2.0
±
2.5 LSB(max)
±
1.0 LSB(max)
±
2.8
±
0.6
1.8
2.2
12 pF
28 pF
2.00
1.8
2.2
3.5 KΩ
80 77 dB(min)
79 76 dB(min)
12.8 12.3 Bits(min)
−88 −80 dB(min)
90 dB
−97 dB
Units
%
FS(max)
%
FS(max)
V(min)
V(max)
V(min)
V(max)
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ADC14161
DC and Logic Electrical Characteristics
The following specifications apply for AGND=DGND=DGND I/O=0V, V
PD=+5V, V
Boldface limits apply for T
Symbol Parameter Conditions
CLOCK, RD, PD Digital Input Characteristics
V
IN(1)
V
IN(0)
I
IN(1)
I
IN(0)
C
IN
CAL, RESET Digital Input Characteristics
V
IN(1)
V
IN(0)
I
IN(1)
I
IN(0)
C
IN
D00 - D13 Digital Output Characteristics
V
OUT(1)
V
OUT(1)
V
OUT(0)
I
OZ
+I
SC
−I
SC
Power Supply Characteristics
I
A
I
D
I/O
I
D
PSRR
=
+2.0V, V
REF+
Logical ″1″ Input Voltage V
Logical ″0″ Input Voltage V
Logical ″1″ Input Current V
Logical ″0″ Input Current V
REF IN
=
A
T
J
=
AGND, f
=
T
MIN
=
2.5 MHz, RS=25Ω,C
CLK
to T
+
+
IN
IN
: all other limits T
MAX
=
5.25V 2.0 V(min)
=
4.75V 0.8 V(max)
=
5.0V 5 µA
=
0V −5 µA
A
VINInput Capacitance 5 pF
+
Logical ″1″ Input Voltage V
Logical ″0″ Input Voltage V
Logical ″1″ Input Current V
Logical ″0″ Input Current V
=
5.25V 3.5 V(min)
+
=
4.75V 1.0 V(max)
=
5.0V 5 µA
IN
=
0V −5 µA
IN
Input Capacitance 5 pF
Logical ″1″ Output
Voltage
Logical ″1″ Output
Voltage
Logical ″0″ Output
Voltage
TRI-STATE Output
Current
Output Short Circuit
Source Current
Output Short Circuit Sink
Current
V
I/O=4.75V, I
D
V
I/O=2.7V, I
D
I/O=5.25V, I
V
D
V
I/O=3.3V, I
D
=
V
OUT
=
V
OUT
=
V
OUT
=
V
OUT
3V or 5V 100 nA
0V −100 nA
0V, V
D
I/O=3V 12 mA
V
D
=
−360 µA 4.5 V(min)
OUT
=
−360 mA 2.5 V(min)
OUT
=
1.6 mA 0.4 V(max)
OUT
=
1.6 mA 0.4 V(max)
OUT
I/O=3V −10 mA
Analog Supply Current PD=VDI/O 70 85 mA(max)
Digital Supply Current PD=VDI/O 7 8 mA(max)
Output Bus Supply
Current
Total Power
Consumption
Power Supply Rejection
PD=VDI/O 1 2 mA(max)
PD=V
I/O 390 475 mW(max)
D
PD=DGND
250 mV
100kHz riding on V
PP
Ratio
+
=
V
=
50 pF/pin. After Auto-Cal
L
=
=
T
25˚C(Notes 7, 8, 9)
J
A
=
A
=
V
+5.0V, V
D
Typical
(Note 10)
<
2mW
I/O=3.0V or 5.0V,
D
Limits
(Note 11)
54 dB
@
Temperature.
Units
AC Electrical Characteristics
The following specifications apply for AGND=DGND=DGND I/O=0V, V
PD=+5V, V
Boldface limits apply for T
Symbol Parameter Conditions
f
CLK
t
CONV
t
AD
REF
=
+
+2.0V, V
REF IN
=
A
T
=
=
J
AGND, f
to T
T
MIN
=
2.5 MHz, RS=25Ω,C
CLK
: all other limits T
MAX
A
Conversion Clock (CLOCK)
Frequency
Conversion Clock Duty Cycle
Conversion Latency 13 Clock Cycles
Aperture Delay 9 ns
+
=
V
=
50 pF/pin. After Auto-Cal
L
=
=
T
25˚C(Notes 7, 8, 9)
J
=
V
A
D
Typical
(Note 10)
=
+5.0V, V
I/O=3.0V or 5.0V,
D
@
Temperature.
Limits
(Note 11)
Units
(Limits)
300 kHz(min)
3 2.5 MHz(max
45
55
%
%
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(min)
(max)
AC Electrical Characteristics (Continued)
+
=
=
The following specifications apply for AGND=DGND=DGND I/O=0V, V
PD=+5V, V
ADC14161
Boldface limits apply for T
REF
=
+
+2.0V, V
REF IN
=
A
T
=
=
J
AGND, f
to T
T
MIN
=
2.5 MHz, RS=25Ω,C
CLK
: all other limits T
MAX
=
A
V
=
50 pF/pin. After Auto-Cal
L
=
T
25˚C(Notes 7, 8, 9)
J
Symbol Parameter Conditions
t
OD
t
EOCL
t
DATA_VALID
t
AD
t
ON
t
OFF
t
CAL
Note 1: Absolute MaximumRatings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which thedevice is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions.
Note 2: All voltages are measured with respect to GND=AGND=DGND I/O=0V, unless otherwise specified.
Note 3: When the input voltage at any pin exceeds the power supplies (that is, V
The 50 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 25 mA to two.
Note 4: The absolute maximum junction temperature (T
junction-to-ambient thermal resistance (θ
TQFP, θ
device under normal operation will typically be about 410 mW (390 mW quiescent power + 20 mW due to 1 TTL load on each digital output. The values for maximum
power dissipation listed above will be reached only when the ADC14161 is operated in a severe fault condition (e.g. when input or output pins are driven beyond the
power supply voltages, or the power supply polarity is reversed). Obviously, such conditions should always be avoided.
Note 5: Human body model is 100 pF capacitor discharged through a 1.5kΩ resistor. Machine model is 220 pF discharged through ZERO Ω.
Note 6: See AN450, ″Surface Mounting Methods and Their Effect on Product Reliability″, or the section entitled ″Surface Mount″ found in any post 1986 National
Semiconductor Linear Data Book, for other methods of soldering surface mount devices.
Note 7: The inputs are protected as shown below. Input voltage magnitudes up to 5V above V
is limited per Note 3. However, errors in the A/D conversion can occur if the input goes above V
V
is 70˚C/W, so PDMAX = 1,785 mW at 25˚C and 982 mW at the maximum operating ambient temperature of 85˚C. Note that the power dissipation of this
JA
, the full-cale input voltage must be ≤4.85VDCto ensure accurate conversions
DC
Falling edge of CLK to Data
Valid
Falling edge of CLK to falling
edge of EOC
Falling edge of CLOCK to Data
Valid
Aperture Delay 9 ns
RD low to data valid on D00
-D13
RD high to D00 -D13 in
TRI-STATE
Calibration Time 110 ms
<
AGND or V
IN
max) for this device is 150˚C. The maximum allowable power dissipation is dictated by TJmax, the
), and the ambient temperature (TA), and can be calculated using the formula PDMAX=(TJmax - TA)/θJA. In the 52-pin
JA
J
>
VAor VD), the current at that pin should be limited to 25 mA.
IN
or to 5V below GND will not damage this device, provided current
A
or below GND by more than 100 mV.As an example, if VAis 4.75
A
V
A
D
Typical
(Note 10)
=
+5.0V, V
I/O=3.0V or 5.0V,
D
@
Temperature.
Limits
(Note 11)
50 ns
1/(4f
1/(8f
CLK
CLK
)
)
90
130
38
95
23 33 ns(max)
25 33 ns(max)
Units
(Limits)
ns(min)
ns(max)
ns(min)
ns(max)
DS100154-12
DS100154-11
ESD Protection Scheme for Analog Input and Digital
Output pins
ESD Protection Scheme for Digital Input pins
Note 8: To guarantee accuracy, it is required that V
Note 9: With the test condition for V
Note 10: Typical figures are at T
Note 11: Tested limits are guaranteed to Nationsl’s AOQL (Average Outgoing Quality Level).
Note 12: Integral Non Linearity is defined as the deviation of the analog value, expressed in LSBs, from the straight line that passes through positive full-scale and
negative full-scale.
Note 13: Timing specifications are tested at the TTL logic levels, V
to 1.4V.
Note 14: Optimum SNR performance will be obtained by keeping the reference input in the 1.8V to 2.2V range. The LM4041CIM3-ADJ (SOT-23 package) or the
LM4041CIZ-ADJ (TO-92 package), bandgap voltage reference is recommended for this application.
=
REF
=
=
T
25˚C, and represent most likely parametric norms.
A
J
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and VDbe connected together and to the same power supply with separate bypass capacitors at each V+pin.
A
+−V
(V
REF
−) given as +2.0V, the 14-bit LSB is 122 µV.
REF
=
0.4V for a falling edge and V
IL
=
2.4V for a rising edge. TRI-STATE output voltage is forced
IH
AC Electrical Characteristics (Continued)
ADC14161
FIGURE 1. Transfer Characteristics
FIGURE 2. Simplified Error Curve vs. Output Code after Auto-Cal cycle
DS100154-13
DS100154-14
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Typical Performance Characteristics
INL vs Temperature
ADC14161
INL vs V
and Temperature
REF
DS100154-25
DS100154-35
DNL vs Temperature
DNL vs V
and Temperature
REF
DS100154-26
DS100154-34
SNR vs Temperature
DS100154-27
THD vs Temperaure
DS100154-28
SINAD & ENOB vs Temperature
DS100154-29
IMD
SINAD & ENOB vs Clock Duty
Cycle
DS100154-30
Spectral Response
SFDR vs Temperature and f
IN
DS100154-31
DS100154-32
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DS100154-33
Specification Definitions
APERTURE JITTER is the variation in aperture delay from
sample to sample. Aperture jitter shows up as input noise.
APERTURE DELAY is the time required after the falling
edge of the clock for the sampling switch to open. In other
words, for the Track/Hold circuit to go from ″track″ mode into
the ″hold″ mode. The Track/Hold circuit effectively stops
capturing the input signal and goes into the ″hold″ mode t
after the fall of the clock.
OFFSET ERROR is the difference between the ideal LSB
transition to the actual transition point. The LSB transition
should occur when V
+=VIN−.
IN
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of
the maximum deviation from the ideal step size of 1 LSB.
EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE
BITS) is another method of specifying Signal-to-Noise and
Distortion Ratio, or SINAD. ENOB is defined as (SINAD
−1.76) / 6.02.
FULL SCALE ERROR is the difference between the input
voltage [(V
full scale and V
(V
REF−IN
+)−(VIN−)] just causing a transition to positive
IN
− 1.5 LSB, where V
REF
REF
is(V
).
FULL POWER BANDWIDTH is a measure of the frequency
at which the reconstructed output fundamental drops 3 dB
below its low frequency value for a full scale input. The test
is performed with f
of f
. The input frequency at which the output is −3 dB
CLK
equal to 100 kHz plus integral multiples
IN
relative to the low frequency input signal is the full power
bandwidth.
INTERMODULATION DISTORTION (IMD) is the creation of
additional spectral components as a result of two sinusoidal
frequencies being applied to the ADC input at the same time.
REF+IN
AD
)−
It is defined as the ratio of the power in the intermodulation
products to the total power in the original frequencies. IMD is
usually expressed in dB.
INTEGRAL NON-LINEARITY (INL) is a measure of the deviation of each individual code from a line drawn from negative full scale (
1
⁄2LSB below the first code transition) through
positive full scale (the last code transition). The deviation of
any given code from this straight line is measured from the
center of that code value.
PIPELINE DELAY (LATENCY) is the number of clock cycles
between initiation of conversion and when that data is presented to the output stage. Data for any given sample is
available the Pipeline Delay plus the Output Delay after that
sample is taken. New data is available at every clock cycle,
but the data lags the conversion by the pipeline delay.
SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in
dB, of the rms value of the input signal to the rms value of the
sum of all other spectral components below one-half the
sampling frequency, not including harmonics or dc.
SIGNAL TO NOISE PLUS DISTORTION (S/(N+D) or SINAD)) Is the ratio, expressed in dB, of the rms value of the
input signal to the rms value of all of the other spectral components below half the clock frequency, including harmonics
but excluding dc.
SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the rms values of the input
signal and the peak spurious signal, where a spurious signal
is any signal present in the output spectrum that is not
present at the input.
TOTAL HARMONIC DISTORTION (THD) is the ratio, expressed in dB or dBc, of the rms total of the first six harmonic
components, to the rms value of the input signal.
ADC14161
Timing Diagrams
TIMING DIAGRAM 1. Output Timing
DS100154-15
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Timing Diagrams (Continued)
ADC14161
DS100154-16
TIMING DIAGRAM 2. Reset and Calibration
www.national.com 12
Functional Description
Operating on a single +5V supply, the ADC14161 uses a
pipelined architecture and has error correction circuitry and a
calibration mode to help ensure maximum performance at all
times.
Balanced analog signals with a peak-to-peak voltage equal
to the input reference voltage, V
the common mode input voltage, V
(13 bits plus sign). Neglecting offsets, positive input signal
voltages (V
+−VIN−>0) produce positive digital output
IN
data and negative input signal voltages (V
produce negative output data. The input signal can be digitized at any clock rate between 300 Ksps and 2.5 Msps.
Input voltages below the negative full scale value will cause
the output word to take on the negative full scale value of
10,0000,0000,0000. Input voltage above the positive full
scale value will cause the output word to take on the positive
full scale value of 01,1111,1111,1111.
The output word rate is the same as the clock frequency.The
analog input voltage is acquired at the falling edge of the
clock and the digital data for that sample is delayed by the
pipeline for 13 clock cycles plus t
put is undefined if the chip is being reset or is in the calibration mode. The output signal may be inhibited by the RD pin
while the converter is in one of these modes.
The RD pin must be low to enable the digital outputs. A logic
low on the power down (PD) pin reduces the converter
power consumption to less than two milliwatts.
, and centered around
REF
, are digitized to 14 bits
CM
+−VIN−<0)
IN
DATA_VALID
. The digital out-
V
REF (MID)
V
CM
is the reference mid-point and is derived from
. This point is brought out only to be by passed. By pass
this pin with 0.1µF capacitor to ground. Do not load this pin.
It is very important that all grounds associated with the refer-
ence voltage make connection to the analog ground plane at
a single point to minimize the effects of noise currents in the
gound path.
1.3 Signal Inputs
The signal inputs are V
+ and VIN−. The signal input, VIN,
IN
is defined as
=
V
IN
Figure 3
indicates the relationship between the input voltage
and the reference voltages.
+)−(VIN−).
(V
IN
Figure 4
shows the expected in-
put signal range.
ADC14161
Applications Information
1.0 OPERATING CONDITIONS
We recommend that the following conditions be observed for
operation of the ADC14161:
4.75V ≤ V
5.25V ≤ V
3.0V ≤ V
0.3MHz ≤ f
V
CM
V
REF IN
V
REF IN
1.1 The Analog Inputs
TheADC14161 has two analog signal inputs, V
These two pins form a balanced signal input. There are two
reference pins, V
differential input reference.
1.2 Reference Inputs
V
should always be more positive than V
REF+IN
effective reference voltage, V
these two voltages:
The operational voltage range of V
+3.0 Volts. The operational voltage range of V
ground to 1.0V. For best performance, the difference between V
REF+IN
of 1.8V to 2.2V. Reducing the reference voltage below 1.8V
will decrease the signal-to-noise ratio (SNR) of the
ADC14161. Increasing the reference voltage (and, consequently, the input signal swing) above 2.2V will increase
THD.
≤ 5.25V
A
≤ 5.25V
D
I/O ≤ VD
D
CLK
=
2.0V (forced)
+=2.0V
−=AGND
REF+IN
=
V
REF
and V
≤ 2.5 MHz
and V
REF
(V
REF−IN
)−(V
REF+IN
should remain within the range
. These pins form a
REF−IN
, is the difference between
REF−IN
REF+IN
+ and VIN−.
IN
. The
REF−IN
).
is +1.8 Volts to
REF−IN
DS100154-17
FIGURE 3. Typical Input to Reference Relationaship.
DS100154-18
FIGURE 4. Expected Input Signal Range.
The ADC14161 performs best with a balanced input cen-
is
tered around V
V
+orVIN− should be less than the reference voltage and
IN
each signal input pin should be centered on the V
The two V
. The peak-to-peak voltage swing at either
CM
voltage.
-centered input signals should be exactly 180˚
CM
CM
out of phase from each other. As a simple check to ensure
this, be certain that the average voltage at the ADC iinput
pins is equal to V
. Drive the analog inputs with a source
CM
impedance less than 100 Ohms.
www.national.com13
Applications Information (Continued)
The sign bit of the output word will be a logic low when V
is greater than V
ADC14161
bit of the output word will be a logic high.
For single ended operation, one of the analog inputs should
be connected to V
duced by about 12dB with a single ended input as compared
with differential inputs.
An input voltage of V
preted as mid-scale and will thus be converted to
00,0000,0000,0000, plus any offset error.
The V
+ and the VIN− inputs of the ADC14161 consist of an
IN
analog switch followed by a switched-capacitor amplifier.
The capacitance seen at the analog input pins changes with
the clock level, appearing as 12 pF when the clock is low,
and 28 pF when the clock is high. It is recommended that the
ADC14161 be driven with a low impedance source of 100
Ohms or less.
Asimple application circuit is shown in
Here we use two LM6172 dual amplifiers to provide a balanced input to the ADC14161. Note that better noise performance is achieved when V
well-bypassed resistive divider. The resulting offset and offset drift is minimal.
Since a dynamic capacitance is more difficult to drive than is
a fixed capacitance, choose driving amplifiers carefully. The
CLC427, CLC440, LM6152, LM6154, LM6172, LM6181 and
LM6182 are excellent amplifiers for driving the ADC14161.
1.4 V
The V
of the V
The V
Analog Inputs
CM
input of the ADC14161 is internally biased to 40
CM
supply with on-chip resistors, as shown in
A
pin must be bypassed to prevent any power supply
CM
noise from modulating this voltage. Modulation of the V
potential will result in the introduction of noise into the input
signal. The advantage of simply bypassing V
driving it) is the circuit simplicity.On the other hand, if the V
supply can vary for any reason, VCMwill also vary at a rate
and amplitude related to the RC filter created by the bypass
capacitor and the internal divider resistors. However, performance of this approach will be adequate for many
applications.
FIGURE 5. VCMinput to the ADC14161 VCMis set to
40%of V
improved when V
By forcing V
lems mentioned above. One such approach is to buffer the
2.0 Volt reference voltage to drive the V
a constant potential as shown in
reference voltage is different from the desired V
sired V
voltage may be derived from the reference or from
CM
another stable source.
− . When VIN+ is less than VIN−, the sign
IN
. However, SNR and SINAD are re-
CM
=
+)−(VIN−)=0 will be inter-
(V
IN
IN
Figure 6
REF+IN
with on-chip resistors. Performance is
A
is driven with a stable, low
CM
voltage is forced with a
DS100154-21
impedance source
to a fixed potential, you can avoid the prob-
CM
input, holding it at
CM
Figure 6
and
Figure 8
and
CM
CM
IN
Figure 7
%
Figure 5
CM
(without
.Ifthe
, that de-
Note that the buffer used for this purpose should be a slow,
low noise amplifier. The LMC660, LMC662, LMC272 and
+
LMC7101 are good choices for driving the V
CM
pin of the
ADC14161.
If it is desired to use a multiplexer at the analog input, that
multiplexer should be switched at the rising edge of the clock
signal.
2.0 DIGITAL INPUTS
Digital Inputs consist of CLOCK, RESET, CAL, RD and PD.
All digital input pins should remain stable from the fall of the
clock until 30ns after the fall of the clock to minimize digital
noise corruption of the input signal on the die.
2.1 The CLOCK signal drives an internal phase delay loop to
create timing for theADC. Drive the clock input with a stable,
low phase jitter clock signal in the range of 300 kHz to 2.5
MHz. The trace carrying the clock signal should be as short
as possible. This trace should not cross any other signal line,
analog or digital, not even at 90˚.
.
The CLOCK signal also drives the internal state machine. If
the clock is interrupted, the data within the pipeline could become corrupted.
A 100 Ohm damping resistor should be placed in series with
the CLOCK pin to prevent signal undershoot at that input.
2.2 The RESET input is level sensitive and must be pulsed
high for at least two clock cycles to reset the ADC after
power-up and before calibration (See Timing Diagram 2).
2.3 The CAL input is level sensitive and must be pulsed high
for at least two clock cycles to begin ADC calibration (See
Timing Diagram 2). Reset the ADC14161 before calibrating.
Re-calibrate after the temperature has changed by more
.
than 50˚C since the last calibration was performed and after
return from power down.
During calibration, use the same clock frequency that will be
used for conversions to avoid excessive offset errors.
A
Calibration takes 272,800 clock cycles. Irrelevant data may
appear at the data outputs during RESET or CAL and for 13
clock cycles thereafter.Calibration should not be started until
the reference outputs have settled (100mS with 1µF capacitors on these outputs) after power up or coming out of the
power down mode.
2.4 RD pin is used to READ the conversion data. When the
RD pin is low, the output buffers go into the active state.
When the RD input is high, the output buffers are in the high
impedance state.
2.5 The PD pin, when low, holds the ADC14161 in a
power-down mode where power consumption is typically
less than 2mW to conserve power when the converter is not
being used. The ADC14161 will begin normal operation
within t
after this pin is brought high, provided a valid
WU
CLOCK input is present. Power dissipation during shut-down
is not affected by the clock frequency, or by whether there is
a clock signal present. The data in the pipeline is corrupted
while in the power down mode.The ADC14161 should be reset and calibrated upon returning to normal operation after a
power down.
3.0 OUTPUTS
The ADC14161 has four analog outputs: V
V
REF−OUT,VREF (MID)
and VCM.There are 15 digital outputs:
REF+OUT
,
EOC (End of Conversion) and 14 Data Output pins.
www.national.com 14
Applications Information (Continued)
3.1 The reference output voltages are made available only
for the purpose of bypassing with capacitors. These pins
should not be loaded with more than 10 µADC. These output
voltages are described as
V
REF+OUT
V
REF−OUT
where V
V
REF (MID)
REF
=
To avoid signal clipping and distortion, V
exceed 3.3V, V
V
should be held in the range of 1.8V to 2.2V.
CM
REF−OUT
3.2 The /EOC output goes low to indicate the presence of
valid data at the output data lines. Valid data is present the
entire time that this signal is low except during reset. Corrupt
or irrelevant data may appear at the data outputs when the
RESET pin or the CAL pin is high.
3.3 The Data Outputs are TTL/CMOS compatible. The output data format is two’s complement. Valid data is present at
these outputs while the EOC pin is low. While the t
and the t
DATA_VALID
timing, a simple way to capture a valid output is to latch the
data on the rising edge of the CLOCK (pin 10).
Also helpful in minimizing noise due to output switching is to
minimize the load currents at the digital outputs. This can be
done by connecting buffers between the ADC outputs and
any other circuitry. Only one input should be connected to
=
+1⁄2V
V
CM
=
V
CM
=
(V
REF+IN
(V
REF+OUT+VREF−OUT
−1⁄2V
)−(V
REF
REF
+ IN)
REF
REF+OUT
)/2.
should not
should not be below 750 mV and
time
EOCL
time provide information about output
each output pin. Additionally, inserting series resistors of 47
or 56 Ohms at the digital outputs, close to the ADC pins, will
isolate the outputs from other circuitry and limit output currents. (See
Figure 6
).
4.0 POWER SUPPLY CONSIDERATIONS
Each power supply pin should be bypassed with a parallel
combination of a 10 µF capacitor and a 0.1 µF ceramic chip
capacitor.The chip capacitors should be within
1
⁄2centimeter
of the power pins. Leadless chip capacitors are preferred because they provide low lead inductance.
While a single 5V source is used for the analog and digital
supplies of the ADC14161, these supply pins should be well
isolated from each other to prevent any digital noise from being coupled to the analog power pins. Supply isolation with
ferrite beads is shown in
Figure 6
and
Figure 8
.
As is the case with all high-speed converters, the ADC14161
is sensitive to power supply noise. Accordingly, the noise on
the analog supply pin should be kept below 100 mV
P-P
.
No pin should ever have a voltage on it that is in excess of
the supply voltages, not even at power up.
The V
I/O provides power for the output drivers and may be
D
operated from a supply in the range of 3.0V to the V
supply
D
(nominal 5V). This can simplify interfacing to 3.0 Volt devices
and systems. Powering V
I/O from 3 Volts will also reduce
D
power consumption and noise generation due to output
switching. DO NOT operate the V
than V
or VA.
D
I/O at a voltage higher
D
ADC14161
FIGURE 6. Simple application circuit with single-ended to differential buffer.
DS100154-19
www.national.com15
Applications Information (Continued)
ADC14161
FIGURE 7. Differential drive circuit of
Figure 6
DS100154-20
. All 5k resistors are 0.1%. Tolerance of the other resistors is not
critical.
FIGURE 8. Driving the signal inputs with a transformer.
www.national.com 16
DS100154-22
Applications Information (Continued)
5.0 LAYOUT AND GROUNDING
Proper grounding and proper routing of all signals are essential to ensure accurate conversion. Separate analog and
digital ground planes that are connected beneath the
ADC14161 are required to achieve specified performance.
The analog and digital grounds may be in the same layer,but
should be separated from each other and should never overlap each other. Separation should be at least
possible.
The ground return for the digital supply (DGND I/O ) carries
the ground current for the output drivers. This output current
can exhibit high transients that could add noise to the conversion process. To prevent this from happening, the DGND
I/O pin should NOT be connected in close proximity to any of
the ADC14161’s ground pins.
Capacitive coupling between the typically noisy digital
ground plane and the sensitive analog circuitry can lead to
poor performance that may seem impossible to isolate and
remedy. The solution is to keep the analog circuitry separated from the digital circuitry and from the digital ground
plane.
Digital circuits create substantial supply and ground current
transients. The logic noise thus generated could have significant impact upon system noise performance. The best logic
family to use in systems with A/D converters is one which
employs non-saturating transistor designs, or has low noise
characteristics, such as the 74LS, 74HC(T) and 74AC(T)Q
families. The worst noise generators are logic families that
draw the largest supply current transients during clock or signal edges, like the 74F and the 74AC(T) families.
Since digital switching transients are composed largely of
high frequency components, total ground plane copper
weight will have little effect upon the logic-generated noise.
This is because of the skin effect. Total surface area is more
important than is total ground plane volume.
An effective way to control ground noise is by connecting the
analog and digital ground planes together beneath the ADC
with a copper trace that is very narrow compared with the
1
⁄8inch, where
rest of the ground plane. A typical width is 3/16 inch (4 to 5
mm).This narrowing beneath the converter provides a fairly
high impedance to the high frequency components of the
digital switching currents, directing them away from the analog pins. The relatively lower frequency analog ground currents see a relatively low impedance across this narrow
ground connection.
Generally,analog and digital lines should cross each other at
90 degrees to avoid getting digital noise into the analog path.
To maximize accuracy in high speed, high resolution systems, however, avoid crossing analog and digital lines altogether. It is important to keep any clock lines isolated from
ALL other lines, including other digital lines. Even the generally accepted 90 degree crossing should be avoided as even
a little coupling can cause problems at high frequencies.
This is because other lines can introduce phase noise (jitter)
into the clock line, which can lead to degradation of SNR.
Best performance at high frequencies and at high resolution
is obtained with a straight signal path. That is, the signal path
through all components should form a straight line wherever
possible.
Be especially careful with the layout of inductors. Mutual inductance can change the characteristics of the circuit in
which they are used. Inductors should not be placed side by
side, even with just a small part of their bodies beside each
other.
The analog input should be isolated from noisy signal traces
to avoid coupling of spurious signals into the input. Any external component (e.g., a filter capacitor) connected between the converter’s input and ground should be connected
to a very clean point in the analog ground plane.
Figure 9
cuitry (input amplifiers, filters, reference components, etc.)
should be placed on or over the analog ground plane. All
digital circuitry and I/O lines should be placed over the digital
ground plane.
All ground connections should have a low inductance path to
ground.
gives an example of a suitable layout.All analog cir-
ADC14161
www.national.com17
Applications Information (Continued)
ADC14161
FIGURE 9. Example at a suitable layout.
6.0 DYNAMIC PERFORMANCE
The ADC14161 can achieve impressive dynamic performance. To achieve the best dynamic performance with the
ADC14161, the clock source driving the CLK input must be
free of jitter. For best ac performance, isolate the ADC clock
from any digital circuitry with buffers, as with the clock tree
shown in
Figure 10
.
As mentioned in section 5.0, it is good practice to keep the
ADC clock line as short as possible and to keep it well away
from any other signals. Other signals can introduce phase
noise (jitter) into the clock signal, which can lead to increased distortion. Even lines with 90˚ crossings have capacitive coupling, so try to avoid even these 90˚ crossings of
the clock line.
DS100154-24
FIGURE 10. Isolating the ADC clock from other
circuitry with a clock tree.
DS100154-23
7.0 COMMON APPLICATION PITFALLS
Driving the inputs (analog or digital) beyond the power
supply rails. For proper operation, all inputs should not go
more than 100 mV beyond the supply rails (more than 100
mV below the ground pins or 100 mV above the supply pins).
Exceeding these limits on even a transient basis may cause
faulty or erratic operation. It is not uncommon for high speed
digital circuits (e.g., 74F and 74AC devices) to exhibit undershoot that goes more than a volt below ground. A resistor of
about 50 to 100Ω in series with the offending digital input will
eliminate the problem.
Do not allow input voltages to exceed the supply voltage during power up.
Be careful not to overdrive the inputs of the ADC14161 with
a device that is powered from supplies outside the range of
theADC14161 supply. Such practice may lead to conversion
inaccuracies and even to device damage.
Attempting to drive a high capacitance digital data bus.
The more capacitance the output drivers must charge for
each conversion, the more instantaneous digital current
flows through V
I/O and DGND I/O. These large charging
D
current spikes can couple into the analog circuitry of the
ADC14161, degrading dynamic performance. Adequate bypassing and maintaining separate analog and digital ground
planes will reduce this problem. The digital data outputs
should be buffered (with 74ACQ541, for example). Dynamic
performance can also be improved by adding series resistors at each digital output, close to the ADC14161, which reduces the energy coupled back into the converter output
pins by limiting the output current. A reasonable value for
these resistors is 47Ω.
Using an inadequate amplifier to drive the analog input.
As explained in Section 1.2, the capacitance seen at the in-
www.national.com 18
Applications Information (Continued)
put alternates between 12 pF and 28 pF,depending upon the
phase of the clock. This dynamic loaad is more difficult to
drive than is a fixed capacitance.
If the amplifier exhibits overshoot, ringing, or any evidence of
instability, even at a very low level, it will degrade performance. Amplifiers that have been used sucessfully to dirve
the analog inputs of the ADC14161 include the CLC427,
CLC440, LM6152, LM6154, LM6181 and the LM6182. A
small series reistor at each amplifier output and a capacitor
across the analog inputs (as shown in
prove performance.
Operating with the reference pins outside of the specified range. As mentioned in section 1.1, V
the range of
Figure 7
REF
) will often im-
should be in
REF
≤ 2.2V
with V
1.8V ≤ V
≤ 1.0V. Operating outside of these limits could
REF−IN
lead to signal distortion.
Using a clock source with excessive jitter, using excessively long clock signal trace, or having other signals
coupled to the clock signal trace. This will cause the sam-
pling interval to vary, causing excessive output noise and a
reduction in SNR performance.
Connecting pins marked ″NC″ to any potential. Some of
these pins are used for factory testing. They should all be left
floating. Connecting them to ground, power supply, or some
other voltage could result in a non-functional device.
ADC14161
www.national.com19
Physical Dimensions inches (millimeters) unless otherwise noted
52-Lead Thin Quad Flat Pack
Ordering Information Package ADC14161CIVT
NS Package Number VEG52A
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ADC14161 Low-Distortion, Self-Calibrating 14-Bit, 2.5 MSPS, 390 mW A/D Converter
whose failure to perform when properly used in
accordance with instructions for use provided in the
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