LT1228
100MHz Current Feedback
Amplifier with DC Gain Control
FEATURES DESCRIPTION Very Fast Transconductance Amplifier Bandwidth: 75MHz gm = 10 × ISET Low THD: 0.2% at 30mVRMS Input Wide ISET Range: 1µA to 1mA
n 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
n Wide Supply Range: ±2V to ±15V
n Inputs Common Mode to Within 1.5V of Supplies
n Outputs Swing Within 0.8V of Supplies
n Supply Current: 7mA
n Available in 8-Lead PDIP and SO Packages 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. n 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, 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. APPLICATIONS n n n n n n The LT1228 current feedback amplifier has very high input …