The LMH6518 is a digitally controlled variable gain amplifier whose total gain can be varied from –1.16 dB to 38.8 dB for a 40 dB range in 2 dB steps. The –3 dB bandwidth is 900 MHz at all gains. Gain accuracy at each setting is typically 0.1 dB. When used in conjunction with a Texas Instruments Gsample/second (Gsps) ADC with adjustable full scale (FS) range, the LMH6518 gain adjustment will accommodate full scale input signals from 6.8 mVPP to 920 mVPP to get 700 mVPP nominal at the ADC input. The Auxiliary output (&qupt;+OUT Aux"\x9D and "–OUT Aux") follows the Main output and is intended for use in Oscilloscope trigger function circuitry but may have other uses in other applications.
The LMH6518 gain is programmed via a SPI-1 compatible serial bus. A signal path combined gain resolution of 8.5 mdB can be achieved when the LMH6518’s gain and the Gsps ADC’s FS input are both manipulated. Inputs and outputs are DC-coupled. The outputs are differential with individual Common Mode (CM) voltage control (for Main and Auxiliary outputs) and have a selectable bandwidth limiting circuitry (common to both Main and Auxiliary) of 20, 100, 200, 350, 650, 750 MHz or full bandwidth.
Gain Range 40 dB
Gain Step Size 2 dB
Combined Gain Resolution with Gsample/Second ADC’s 8.5 mdB
Min Gain –1.16 dB
Max Gain 38.8 dB
–3 dB BW 900 MHz
Rise/Fall Time <500 ps
Recovery Time <5 ns
Propagation Delay Variation 100 ps
HD2 @ 100 MHz –50 dBc
HD3 @ 100 MHz –53 dBc
Input-Referred Noise (Max Gain) 0.98 nV/√Hz
Over-Voltage Clamps for Fast Recovery
Power Consumption — Auxiliary Turned Off 1.1W0.75W