The LMH6518 device is a digitally controlled variable gain amplifier whose total gain is
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 TI's
Gsample/second (Gsps) ADC with adjustable full-scale (FS) range, the LMH6518 gain adjustment
accommodates full scale input signals from 6.8 mVPP to 920
mVPP to get 700 mVPP nominal at the ADC input. The auxiliary output (+OUT AUX 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 through a SPI-1 compatible serial bus. A signal path
combined gain resolution of 8.5 mdB is achieved when the device'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.
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