LT1228 - 100MHz Current Feedback Amplifier with DC Gain Control


  • Very Fast Transconductance Amplifier Bandwidth: 75MHz
  • Outputs Swing Within 0.8V of Supplies
  • gm = 10 x 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: 25M Ohm, 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

Typical Application

LT1228 Typical Application
LT1228 Typical Application


TheLT1228 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.


CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.

For complete and up to date package information and drawings, please refer to our packaging page

Part Number Package Code Temp Package
LT1228CN8#PBF N-8 N C 05-08-1510 (N8) Yes
LT1228CS8#PBF SO-8 S8 C 05-08-1610 (S8) Yes
LT1228CS8#TRPBF SO-8 S8 C 05-08-1610 (S8) Yes
LT1228IN8#PBF N-8 N I 05-08-1510 (N8) Yes
LT1228IS8#PBF SO-8 S8 I 05-08-1610 (S8) Yes
LT1228IS8#TRPBF SO-8 S8 I 05-08-1610 (S8) Yes

LT1228 Package Drawing

Order Info

  • Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
  • Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
  • Please refer to our general ordering information or the product datasheet for more details

Package Variations and Pricing

Part Number Package Temp Price
LT1228CN8#PBF N-8 C $4.58 $3.75 Yes
LT1228CS8#PBF SO-8 C $5.17 $4.20 Yes
LT1228CS8#TRPBF SO-8 C $4.26 Yes
LT1228IN8#PBF N-8 I $5.95 $4.83 Yes
LT1228IS8#PBF SO-8 I $5.95 $4.83 Yes
LT1228IS8#TRPBF SO-8 I $4.89 Yes
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* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Demo Boards

Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.

Part Number Description Price Documentation
DC417B DIP8, MS8, S8, SOT23-6 | Multi-Footprint General Purpose Board for Single Op. Amp $25.00
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Click here to view our complete list of demo boards


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