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 g = 10 I implements gain control with a transconductance ampli- m SET Low THD: 0.2% at 30mV Input fier (voltage to current) whose gain is proportional to an RMS Wide I Range: 1A to 1mA externally controlled current. A resistor is typically used SET 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/s 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: 25M, 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, g , is m n Outputs Swing Within 0.8V of Supplies set by the current that flows into Pin 5, I . The small signal SET n Supply Current: 7mA g is equal to ten times the value of I and this relationship m SET 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 such as cables, with excellent linearity at high frequencies. Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Frequency Response 6 Differential Input Variable Gain Amp V = 15V S 3 R = 100 L 15V 4.7F I = 1mA SET 0 R3A 3 10k 3 7 + + 6 1 R2A g V m + IN 9 10k 2 6 I = 300A V SET 5 CFA OUT 12 4 8 I SET 15 R F 15V 470 R4 R5 18 R3 R2 I = 100A 4.7F 1.24k 10k SET + 100 100 R1 R 21 G HIGH INPUT RESISTANCE 270 10 EVEN WHEN POWER IS OFF 24 R6 18dB < GAIN < 2dB 100k 1M 10M 100M 6.19k V 3V IN RMS LT1228 TA01 FREQUENCY (Hz) LT1228 TA02 1228fd 1 GAIN (dB) +LT1228 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) Supply Voltage ....................................................... 18V TOP VIEW Input Current, Pins 1, 2, 3, 5, 8 (Note 8) .............. 15mA I 1 8 GAIN OUT + Output Short Circuit Duration (Note 2) .........Continuous + IN 2 7 V g m Operating Temperature Range +IN 3 6 V OUT LT1228C ...................................................0C to 70C V 4 5 I SET LT1228I ................................................40C to 85C N8 PACKAGE S8 PACKAGE LT1228M (OBSOLETE) ...................... 55C to 125C 8-LEAD PDIP 8-LEAD PLASTIC SO T = 150C, = 100C/W (N) Storage Temperature Range ..................65C to 150C JMAX JA T = 150C, = 150C/W (N) JMAX JA Junction Temperature Plastic Package ................................................. 150C J8 PACKAGE 8-LEAD CERDIP Ceramic Package (OBSOLETE) ......................... 175C T = 175C, = 100C/W (J) JMAX JA Lead Temperature (Soldering, 10 sec) ...................300C OBSOLETE PACKAGE ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1228CN8 PBF LT1228CN8 TRPBF LT1228CN8 8-Lead Plastic DIP 0C to 70C LT1228IN8 PBF LT1228IN8 TRPBF LT1228IN8 8-Lead Plastic DIP 40C to 85C LT1228CS8 PBF LT1228CS8 TRPBF 1228 8-Lead Plastic SO 0C to 70C LT1228IS8 PBF LT1228IS8 TRPBF 1228I 8-Lead Plastic SO 40C to 85C OBSOLETE PACKAGE LT1228MJ8 LT1228MJ8 TRPBF LT1228MJ8 8-Lead CERDIP 55C to 125C LT1228CJ8 LT1228CJ8 TRPBF LT1228CJ8 8-Lead CERDIP 0C to 70C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on nonstandard lead based finish parts. For more information on lead free part marking, go to: