The VCA810 is a DC-coupled, wideband, continuously variable, voltage-controlled gain
amplifier. The device provides a differential input to single-ended output conversion with a
high-impedance gain control input used to vary the gain over a 40-dB to 40-dB range linear in
Operating from ±5-V supplies, the device gain control voltage adjusts the gain from 40
dB at a 0-V input to 40 dB at a 2-V input. Increasing the control voltage above ground attenuates
the signal path to greater than 80 dB. Signal bandwidth and slew rate remain constant over the
entire gain adjust range. This 40-dB/V gain control is accurate within ±1.5 dB (±0.9 dB for high
grade), allowing the gain control voltage in an AGC application to be used as a received signal
strength indicator (RSSI) with ±1.5-dB accuracy.
Excellent common-mode rejection and common-mode input range at the two high-impedance
inputs allow the device to provide a differential receiver operation with gain adjust. The output
signal is referenced to ground. Zero differential input voltage gives a 0-V output with a small DC
offset error. Low input noise voltage ensures good output SNR at the highest gain settings.
In applications where pulse edge information is critical, and the device is being used to
equalize varying channel loss, minimal change in group delay over gain setting retains excellent
pulse edge information.
An improved output stage provides adequate output current to drive the most demanding
loads. Although principally intended to drive analog-to-digital converters (ADCs) or second-stage
amplifiers, the ±60-mA output current easily drives doubly-terminated 50-Ω lines or a passive
post-filter stage over the ±1.7-V output voltage range.
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