Datasheet LT1228 (Analog Devices)

LT1228 100MHz Current Feedback Amplifier with DC Gain Control
FEATURES DESCRIPTION
n Very Fast Transconductance Amplifier The LT®1228 makes it easy to electronically control the Bandwidth: 75MHz gain of signals from DC to video frequencies. The LT1228 gm = 10 × ISET implements gain control with a transconductance ampli- Low THD: 0.2% at 30mVRMS Input fier (voltage to current) whose gain is proportional to an Wide ISET Range: 1µA to 1mA externally controlled current. A resistor is typically used n Very Fast Current Feedback Amplifier to convert the output current to a voltage, which is then Bandwidth: 100MHz amplified with a current feedback amplifier. The LT1228 Slew Rate: 1000V/µs combines both amplifiers into an 8-pin package, and oper- Output Drive Current: 30mA ates on any supply voltage from 4V (±2V) to 30V (±15V). Differential Gain: 0.04% A complete differential input, gain controlled amplifier can Differential Phase: 0.1° be implemented with the LT1228 and just a few resistors. High Input Impedance: 25MΩ, 6pF The LT1228 transconductance amplifier has a high imped- n Wide Supply Range: ±2V to ±15V ance differential input and a current source output with wide n Inputs Common Mode to Within 1.5V of Supplies output voltage compliance. The transconductance, gm, is n Outputs Swing Within 0.8V of Supplies set by the current that flows into Pin 5, ISET. The small signal n Supply Current: 7mA gm is equal to ten times the value of ISET and this relationship n Available in 8-Lead PDIP and SO Packages holds over several decades of set current. The voltage at Pin 5 is two diode drops above the negative supply, Pin 4.
APPLICATIONS
The LT1228 current feedback amplifier has very high input n Video DC Restore (Clamp) Circuits impedance and therefore it is an excellent buffer for the out- n Video Differential Input Amplifiers put of the transconductance amplifier. The current feedback n Video Keyer/Fader Amplifiers amplifier maintains its wide bandwidth over a wide range of n AGC Amplifiers voltage gains making it easy to interface the transconduc- n Tunable Filters tance amplifier output to other circuitry. The current feed- n Oscillators back amplifier is designed to drive low impedance loads, L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. such as cables, with excellent linearity at high frequencies.
TYPICAL APPLICATION Frequency Response
6
Differential Input Variable Gain Amp
VS = ±15V 15V 3 R 4.7µF L = 100Ω + 0 ISET = 1mA R3A 10k 3 –3 + + 7 –6 V R2A g 1 m IN + 10k 2 –9 – – 6 5 CFA V I OUT SET = 300µA 4 GAIN (dB) 8 –12 ISET – R –15V F –15 470Ω R4 R5 –18 R3 R2 4.7µF 1.24k 10k I 100Ω 100Ω + R1 R SET = 100µA G HIGH INPUT RESISTANCE –21 270Ω 10Ω R6 EVEN WHEN POWER IS OFF –24 6.19k –18dB < GAIN < 2dB 100k 1M 10M 100M VIN ≤ 3VRMS LT1228 • TA01 FREQUENCY (Hz) LT1228 • TA02 1228fd 1 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Simplified Schematic Applications Information Typical Applications Package Description Revision History Typical Applications Related Parts