DESCRIPTION
The LT®1228 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.

FEATURES
■ Very Fast Transconductance Amplifier
   Bandwidth: 75MHz
   gm = 10 × ISET
   Low THD: 0.2% at 30mVRMS Input
   Wide ISET Range: 1µA to 1mA
■ Very Fast Current Feedback Amplifier
   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
■ Available in 8-Lead PDIP and SOIC Packages

APPLICATIONS
■ Video DC Restore (Clamp) Circuits
■ Video Differential Input Amplifiers
■ Video Keyer/Fader Amplifiers
■ AGC Amplifiers
■ Tunable Filters
■ Oscillators