Features and Benefits

  • Very Fast Transconductance Amplifier
    • Bandwidth: 75MHz
    • Outputs Swing Within 0.8V of Supplies
    • 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
  • Supply Current: 7mA
  • Available in 8-Lead PDIP and SOIC Packages

Product Details

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 Pin5, ISET. The small signal gm is equal to ten times the value of ISET and this relationship 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.


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

Product Lifecycle icon-recommended Production

At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.

Evaluation Kits (1)

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Pricing displayed is based on 1-piece. The USA list pricing shown is for budgetary use only, shown in United States dollars (FOB USA per unit), and is subject to change. International prices may vary due to local duties, taxes, fees and exchange rates.