Linear Technology LT1228 Datasheet

LT1228

100MHz Current Feedback

Amplifier with DC Gain Control

EATU

F

■

Very Fast Transconductance Amplifier

RE

S

Bandwidth: 75MHz
gm = 10 × I
Low THD: 0.2% at 30mV
Wide I

■

Very Fast Current Feedback Amplifier

SET

Range: 1µA to 1mA

SET

RMS

Input

Bandwidth: 100MHz
Slew Rate: 1000V/µs
Output Drive Current: 30mA
Differential Gain: 0.04%
Differential Phase: 0.1°
High Input Impedance: 25MΩ, 6pF

■

Wide Supply Range: ±2V to ±15V

■

Inputs Common Mode to Within 1.5V of Supplies

■

Outputs Swing Within 0.8V of Supplies

■

Supply Current: 7mA

U

O

PPLICATI

A

■

Video DC Restore (Clamp) Circuits

■

Video Differential Input Amplifiers

■

Video Keyer/Fader Amplifiers

■

AGC Amplifiers

■

Tunable Filters

■

Oscillators

S

DUESCRIPTIO

The LT1228 makes it easy to electronically control the gain
of signals from DC to video frequencies. The LT1228
implements gain control with a transconductance amplifier
(voltage to current) whose gain is proportional to an exter­nally controlled current. A resistor is typically used to
convert the output current to a voltage, which is then
amplified with a current feedback amplifier. The LT1228
combines both amplifiers into an 8-pin package, and oper­ates on any supply voltage from 4V (±2V) to 30V (±15V). A
complete differential input, gain controlled amplifier can be
implemented with the LT1228 and just a few resistors.

The LT1228 transconductance amplifier has a high imped­ance differential input and a current source output with wide
output voltage compliance. The transconductance, gm, is
set by the current that flows into pin 5, I
gm is equal to ten times the value of I
holds over several decades of set current. The voltage at pin
5 is two diode drops above the negative supply, pin 4.

The LT1228 current feedback amplifier has very high input
impedance and therefore it is an excellent buffer for the
output of the transconductance amplifier. The current feed­back amplifier maintains its wide bandwidth over a wide
range of voltage gains making it easy to interface the
transconductance amplifier output to other circuitry. The
current feedback amplifier is designed to drive low imped­ance loads, such as cables, with excellent linearity at high
frequencies.

. The small signal

SET

and this relationship

SET

U

O

A

PPLICATITYPICAL

Differential Input Variable Gain Amp

15V

4.7µF

m

7

4

R4

1.24k

R6

6.19Ω

+

1

+

5

I

SET

R5
10k

R1
270Ω

CFA V

8

–

RG
10Ω

6



R

F

470Ω

HIGH INPUT RESISTANCE
EVEN WHEN POWER IS OFF
–18dB < GAIN < 2dB

≤ 3V

V

IN

RMS

OUT

LT1228 • TA01

R3A
10k

+

R2A

V

IN

10k

–

–15V

100Ω

R3

R2
100Ω

3

+

g

2

–

4.7µF

+

6
3

0
–3
–6
–9

GAIN (dB)

–12
–15
–18
–21

–24

100k

Frequency Response

= 1mA

I

SET

I

= 300µA

SET

I

= 100µA

SET

1M 10M 100M

FREQUENCY (Hz)

= ±15V

V

S

= 100Ω

R

L

LT1228 • TA02

1

LT1228

WU

U

PACKAGE

/

O

RDER I FOR ATIO

W

O

A

LUTEXI T

S

Supply Voltage ...................................................... ±18V

Input Current, Pins 1, 2, 3, 5, 8 (Note 7) ............ ±15mA

Output Short Circuit Duration (Note 1) .........Continuous

Operating Temperature Range

LT1228C................................................ 0°C to 70°C

LT1228M........................................ –55°C to 125°C

Storage Temperature Range ................. –65°C to 150°C

Junction Temperature

Plastic Package .............................................. 150°C

Ceramic Package ............................................175°C

Lead Temperature (Soldering, 10 sec)..................300°C

LECTRICAL C CHARA TERIST

E

Current Feedback Amplifier, Pins 1, 6, 8. ±5V ≤ VS ≤ ±15V, I

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

OS

+

I

IN

–

I

IN

e

n

i

n

R

IN

C

IN

CMRR Common-Mode Rejection Ratio VS = ±15V, V

PSRR Power Supply Rejection Ratio VS = ±2V to ±15V, TA = 25°C6080dB

Input Offset Voltage TA = 25°C ±3 ±10 mV

Input Offset Voltage Drift ● 10 µV/°C
Noninverting Input Current TA = 25°C ±0.3 ±3 µA

Inverting Input Current TA = 25°C ±10 ±65 µA

Input Noise Voltage Density f = 1kHz, RF = 1k, RG = 10Ω, RS = 0Ω 6 nV/√Hz
Input Noise Current Density f = 1kHz, RF = 1k, RG = 10Ω, RS = 10k 1.4 pV/√Hz
Input Resistance V

Input Capacitance (Note 2) VS = ±5V 6 pF
Input Voltage Range VS = ±15V, TA = 25°C ±13 ±13.5 V

Inverting Input Current VS = ±15V, V
Common-Mode Rejection V

Noninverting Input Current VS = ±2V to ±15V, TA = 25°C 10 50 nA/V
Power Supply Rejection V

Inverting Input Current VS = ±2V to ±15V, TA = 25°C 0.1 5 µA/V
Power Supply Rejection VS = ±3V to ±15V ● 5 µA/V

A

WUW

U

ARB

G

I

S

TOP VIEW

1I

OUT

2

–IN
+IN

–

V

J8 PACKAGE

8-LEAD CERAMIC DIP

T

T

J MAX =

T

J MAX =

Consult Factory for Industrial grade parts.

g

m

3

S8 PACKAGE

8-LEAD PLASTIC SOIC

175°C, θ

J MAX =

150°C, θ
150°C, θ

8
7
6
54

N8 PACKAGE

100°C/W (J)
100°C/W (N)
150°C/W (S)

GAIN

+

V
V

OUT

I

SET

+–

8-LEAD PLASTIC DIP

JA =
JA =
JA =

ORDER PART

NUMBER

LT1228MJ8
LT1228CJ8
LT1228CN8
LT1228CS8

S8 PART MARKING

1228

ICS

= 0µA, VCM = 0V unless otherwise noted.

SET

● ±15 mV

● ±10 µA

● ±100 µA

= ±13V, VS = ±15V ● 225 MΩ

IN

= ±3V, VS = ±5V ● 225 MΩ

V

IN

● ±12 V

VS = ±5V, TA = 25°C ±3 ±3.5 V

● ±2V

= ±13V, TA = 25°C5569dB

= ±15V, V

V

S

= ±5V, V

V

S

= ±5V, V

V

S

= ±15V, V

S

= ±5V, V

V

S

VS = ±5V, V

= ±3V to ±15V ● 60 dB

V

S

= ±3V to ±15V ● 50 nA/V

S

CM

= ±12V ● 55 dB

CM

= ±3V, TA = 25°C5569dB

CM

= ±2V ● 55 dB

CM

= ±13V, TA = 25°C 2.5 10 µA/V

CM

= ±12V ● 10 µA/V

CM

= ±3V, TA = 25°C 2.5 10 µA/V

CM

= ±2V ● 10 µA/V

CM

2

LT1228

LECTRICAL C CHARA TERIST

E

Current Feedback Amplifier, Pins 1, 6, 8. ±5V ≤ VS ≤ ±15V, I

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

A

V

R

OL

V

OUT

I

OUT

I

s

SR Slew Rate (Notes 3 and 5) TA = 25°C 300 500 V/µs
SR Slew Rate VS = ±15V, RF = 750Ω, RG= 750Ω, RL = 400Ω 3500 V/µs
t

r

BW Small-Signal Bandwidth VS = ±15V, RF = 750Ω, RG= 750Ω, RL = 100Ω 100 MHz
t

r

t

s

Large-Signal Voltage Gain VS = ±15V, V

Transresistance, ∆V

Maximum Output Voltage Swing VS = ±15V, R

Maximum Output Current R

Supply Current V

Rise Time (Notes 4 and 5) TA = 25°C1020ns

Small-Signal Rise Time VS = ±15V, RF = 750Ω, RG= 750Ω, RL = 100Ω 3.5 ns
Propagation Delay VS = ±15V, RF = 750Ω, RG= 750Ω, RL = 100Ω 3.5 ns
Small-Signal Overshoot VS = ±15V, RF = 750Ω, RG= 750Ω, RL = 100Ω 15 %
Settling Time 0.1%, V
Differential Gain (Note 6) VS = ±15V, RF = 750Ω, RG= 750Ω, RL = 1k 0.01 %
Differential Phase (Note 6) VS = ±15V, RF = 750Ω, RG= 750Ω, RL = 1k 0.01 DEG
Differential Gain (Note 6) VS = ±15V, RF = 750Ω, RG= 750Ω, RL = 150Ω 0.04 %
Differential Phase (Note 6) VS = ±15V, RF = 750Ω, RG= 750Ω, RL = 150Ω 0.1 DEG

OUT

/∆I

–

IN

ICS

= 0µA, VCM = 0V unless otherwise noted.

SET

= ±10V, R

VS = ±5V, V
VS = ±15V, V

= ±5V, V

V

S

= ±5V, R

V

S

LOAD

OUT

OUT

= ±2V, R

OUT

= ±10V, R

OUT

= ±2V, R

OUT

= 400Ω, TA = 25°C ±12 ±13.5 V

LOAD

= 150Ω, TA = 25°C ±3 ±3.7 V

LOAD

= 0Ω, TA = 25°C 30 65 125 mA

= 0V, I

= 0V ● 611 mA

SET

= 10V, RF =1k, RG= 1k, RL =1k 45 ns

OUT

= 1k ● 55 65 dB

LOAD

= 150Ω ● 55 65 dB

LOAD

= 1k ● 100 200 kΩ

LOAD

= 150Ω ● 100 200 kΩ

LOAD

● ±10 V

● ±2.5 V

● 25 125 mA

LECTRICAL C CHARA TERIST

E

Transconductance Amplifier, Pins 1, 2, 3, 5. ±5V ≤ VS ≤ ±15V, I

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

OS

I

OS

I

B

e

n

R

IN

C

IN

Input Offset Voltage I

Input Offset Voltage Drift ● 10 µV/°C
Input Offset Current TA = 25°C 40 200 nA

Input Bias Current TA = 25°C 0.4 1 µA

Input Noise Voltage Density f = 1kHz 20 nV/√Hz
Input Resistance-Differential Mode V
Input Resistance-Common Mode VS = ±15V, VCM = ±12V ● 50 1000 MΩ

Input Capacitance 3pF
Input Voltage Range VS = ±15V, TA = 25°C ±13 ±14 V

ICS

= 100µA, VCM = 0V unless otherwise noted.

SET

= 1mA, TA = 25°C ±0.5 ±5mV

SET

≈ ±30mV ● 30 200 kΩ

IN

= ±5V, VCM = ±2V ● 50 1000 MΩ

V

S

= ±15V ● ±12 V

V

S

= ±5V, TA = 25°C ±3 ±4V

V

S

= ±5V ● ±2V

V

S

● ±10 mV

● 500 nA

● 5 µA

3

LT1228

LECTRICAL C CHARA TERIST

E

Transconductance Amplifier, Pins 1, 2, 3, 5. ±5V ≤ VS ≤ ±15V, I

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

CMRR Common-Mode Rejection Ratio VS = ±15V, V

PSRR Power Supply Rejection Ratio VS = ±2V to ±15V, TA = 25°C 60 100 dB

g

m

I

OUT

I

OL

V

OUT

R

O

I

S

THD Total Harmonic Distortion VIN = 30mV
BW Small-Signal Bandwidth R1 = 50Ω, I
t

r

Transconductance I
Transconductance Drift ● –0.33 %/°C
Maximum Output Current I
Output Leakage Current I

Maximum Output Voltage Swing VS = ±15V , R1 = ∞ ● ±13 ±14 V

Output Resistance VS = ±15V, V

Output Capacitance (Note 2) VS = ±5V 6 pF
Supply Current, Both Amps I

Small-Signal Rise Time R1 = 50Ω, I
Propagation Delay R1 = 50Ω, I

ICS

= 100µA, VCM = 0V unless otherwise noted.

SET

= ±13V, TA = 25°C 60 100 dB

= ±15V, V

V

S

= ±5V, V

V

S

VS = ±5V, V

= ±3V to ±15V ● 60 dB

V

S

= 100µA, I

SET

= 100µA ● 70 100 130 µA

SET

= 0µA (+IIN of CFA), TA = 25°C 0.3 3 µA

SET

= ±5V , R1 = ∞ ● ±3 ±4V

V

S

= ±5V, V

V

S

= 1mA ● 915 mA

SET

CM

= ±12V ● 60 dB

CM

= ±3V, TA = 25°C 60 100 dB

CM

= ±2V ● 60 dB

CM

= ±30µA, TA = 25°C 0.75 1.00 1.25 µA/mV

OUT

● 10 µA

= ±13V ● 28 MΩ

OUT

= ±3V ● 28 MΩ

OUT

at 1kHz, R1 = 100k 0.2 %

RMS

= 500µA 80 MHz

SET

= 500µA, 10% to 90% 5 ns

SET

= 500µA, 50% to 50% 5 ns

SET

The ● denotes specifications which apply over the operating temperature
range.

Note 1: A heat sink may be required depending on the power supply
voltage.

Note 2: This is the total capacitance at pin 1. It includes the input
capacitance of the current feedback amplifier and the output capacitance
of the transconductance amplifier.

Note 3: Slew rate is measured at ±5V on a ±10V output signal while
operating on ±15V supplies with R
slew rate is much higher when the input is overdriven, see the applications
section.

= 1k, RG = 110Ω and RL = 400Ω. The

F

Note 4: Rise time is measured from 10% to 90% on a ±500mV output
signal while operating on ±15V supplies with R
RL = 100Ω. This condition is not the fastest possible, however, it does
guarantee the internal capacitances are correct and it makes automatic
testing practical.

Note 5: AC parameters are 100% tested on the ceramic and plastic DIP
packaged parts (J and N suffix) and are sample tested on every lot of
the SO packaged parts (S suffix).

Note 6: NTSC composite video with an output level of 2V.
Note 7: Back to back 6V Zener diodes are connected between pins 2 and

3 for ESD protection.

= 1k, RG = 110Ω and

F

4

LT1228

TEMPERATURE (°C)

–50

V

–

COMMON-MODE RANGE (V)

0.5

1.0

–1.5

V

+

–25 0 25 125

LT1228 • TPC06

50 75 100

–0.5

–1.0

–2.0

1.5

2.0

V

–

= –2V TO –15V

V+ = 2V TO 15V

INPUT VOLTAGE (mVDC)

–200

0

TRANSCONDUCTANCE (µA/mV)

0.2

0.4

1.4

2.0

–150 –100 –50 200

LT1228 • TPC03

0 100 150

1.8

1.6

1.2

0.6

0.8

–55°C

VS = ±2V TO ±15V
I

SET

= 100µA

50

1.0
25°C

125°C

TEMPERATURE (°C)

–50

V

–

OUTPUT SATURATION VOLTAGE (V)

+0.5

+1.0

–1.0

V

+

–25 0 25 125

LT1228 • TPC09

50 75 100

–0.5

±2V ≤ VS ≤ ±15V
R1 =

∞

UW

Y

PICA

100

10

1

–3dB BANDWIDTH (MHz)

LPER

F

O

R

AT

CCHARA TERIST

E

C

ICS

Transconductance Amplifier, Pins 1, 2, 3 & 5

Small-Signal Bandwidth vs Small-Signal Transconductance Small-Signal Transconductance
Set Current and Set Current vs Bias Voltage vs DC Input Voltage

VS = ±15V

R1 = 100Ω

R1 = 1k

R1 = 10k

R1 = 100k

100

10

0.1

0.01

TRANSCONDUCTANCE (µA/mV)

1

VS = ±2V TO ±15V

= 25°C

T

A

10000

1000

SET CURRENT (µA)

100

10

1.0

0.1
10

Total Harmonic Distortion vs Spot Output Noise Current vs Input Common-Mode Limit vs
Input Voltage Frequency Temperature

10

VS = ±15V

1

I

= 100µA

SET

0.1

OUTPUT DISTORTION (%)

I

= 1mA

SET

0.01
1

INPUT VOLTAGE (mV

Small-Signal Control Path Small-Signal Control Path Output Saturation Voltage vs
Bandwidth vs Set Current Gain vs Input Voltage Temperature

100

VS = ±2V TO ±15V

= 200mV

V

IN

(PIN 2 TO 3)

10

–3dB BANDWIDTH (MHz)

1

10

100 1000

SET CURRENT (µA)

10 1000

∆I
∆I

100 1000

SET CURRENT (µA)

100

OUT
SET

P–P

LT1228 • TPC01

)

LT1228 • TPC04

LT1228 • TPC07

0.001

1.0 1.1 1.4

0.9 1.2 1.3 1.5

BIAS VOLTAGE, PIN 5 TO 4, (V)

1000

100

SPOT NOISE (pA/√Hz)

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

CONTROL PATH GAIN (µA/µA)

0.1

10

10

0

100 10k

FREQUENCY (Hz)

40 80 160

0

INPUT VOLTAGE, PIN 2 TO 3, (mVDC)

VS = ±2V TO ±15V

= 25°C

T

A

I

SET

I

SET

1k 100k

∆I

OUT

∆I

SET



120 200

0.1

LT1228 • TPC02

= 1mA

= 100µA

LT1228 • TPC05

LT1228 • TPC08

5

LT1228

SUPPLY VOLTAGE (±V)

2

–3dB BANDWIDTH (MHz)

40

100

120

12 16

LT1228 • TPC12

4068101418

0

20

60

140

160

180

80

PEAKING ≤ 0.5dB
PEAKING ≤ 5dB

RF = 750Ω

RF = 1k

RF = 2k

RF = 500Ω

SUPPLY VOLTAGE (±V)

2

–3dB BANDWIDTH (MHz)

40

100

120

12 16

LT1228 • TPC15

4068101418

0

20

60

140

160

180

RF = 500Ω

80

PEAKING ≤ 0.5dB
PEAKING ≤ 5dB

RF = 750Ω

RF = 1k

RF = 2k

RF = 250Ω

SUPPLY VOLTAGE (±V)

2

–3dB BANDWIDTH (MHz)

4

10

12

12 16

LT1228 • TPC18

4068101418

0

2

6

14

16

18

RF = 500Ω

8

RF = 1k

RF = 2k

UW

Y

PICA

8
7
6

5
4

3
2

VOLTAGE GAIN (dB)

1
0

–1

–2

0.1 10 100

22
21
20

19
18

17
16

VOLTAGE GAIN (dB)

15
14
13

12

0.1 10 100

LPER

F

O

R

AT

CCHARA TERIST

E

C

ICS

Current Feedback Amplifier, Pins 1, 6, 8

Voltage Gain and Phase vs –3dB Bandwidth vs Supply –3dB Bandwidth vs Supply
Frequency, Gain = 6dB Voltage, Gain = 2, RL = 100Ω Voltage, Gain = 2, RL = 1k

180

160

140

PHASE SHIFT (DEGREES)

120

100

80

60

–3dB BANDWIDTH (MHz)

40

20

0

2

PEAKING ≤ 0.5dB
PEAKING ≤ 5dB

RF = 500Ω

RF = 750Ω

RF = 1k

RF = 2k

4068101418

SUPPLY VOLTAGE (±V)

12 16

LT1228 • TPC11

PHASE

GAIN

VS = ±15V
R

L

= 750Ω

R

F

= 100Ω

1

FREQUENCY (MHz)

0
45
90
135
180
225

LT1228 • TPC10

Voltage Gain and Phase vs –3dB Bandwidth vs Supply –3dB Bandwidth vs Supply
Frequency, Gain = 20dB Voltage, Gain = 10, RL = 100Ω Voltage, Gain = 10, RL = 1kΩ

PHASE

GAIN

VS = ±15V

= 100Ω

R

L

= 750Ω

R

F

1

FREQUENCY (MHz)

0
45
90
135
180
225

LT1228 • TPC13

180

160

PHASE SHIFT (DEGREES)

140

120

100

80

60

–3dB BANDWIDTH (MHz)

40

20

0

2

PEAKING ≤ 0.5dB
PEAKING ≤ 5dB

RF = 250Ω

4068101418

SUPPLY VOLTAGE (±V)

RF = 500Ω

RF = 750Ω

RF = 1k

RF = 2k

12 16

LT1228 • TPC14

Voltage Gain and Phase vs –3dB Bandwidth vs Supply –3dB Bandwidth vs Supply
Frequency, Gain = 40dB Voltage, Gain = 100, RL = 100Ω Voltage, Gain = 100, RL = 1kΩ

42
41
40

39
38

37
36

VOLTAGE GAIN (dB)

35
34
33

32

0.1 10 100

6

PHASE

GAIN

VS = ±15V

= 100Ω

R

L

= 750Ω

R

F

1

FREQUENCY (MHz)

LT1228 • TPC16

0
45
90

PHASE SHIFT (DEGREES)

135
180
225

18

16

14

12

10

–3dB BANDWIDTH (MHz)

8

6

4

2

0

4068101418

2

RF = 500Ω

12 16

SUPPLY VOLTAGE (±V)

RF = 1k

RF = 2k

LT1228 • TPC17