Amplifier with voltage-controlled gain is high speed
20 October 2004Analogue, Mixed Signal, LSI
Products & Solutions
The VCA810 is a DC-coupled, wideband, continuously variable, voltage-controlled gain amplifier from Texas Instruments. It 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 dB/V.
Operating from ±5 V supplies, the gain control voltage for the VCA810 will adjust the gain from -40 dB at 0 V input to +40 dB at -2 V input, says the manufacturer, while increasing the control voltage above ground will attenuate the signal path to >80 dB. Signal bandwidth and slew rate remain constant over the entire gain adjust range. This 40 dB/V gain control is linear to within ±0,5 dB, allowing the gain control voltage in an AGC application to be used as a received signal strength indicator (RSSI) with ±0,5 dB accuracy.
According to the manufacturer, excellent common-mode rejection and common-mode input range at the two high-impedance inputs allows this 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 high gain settings. In applications where pulse edge information is critical, and the VCA810 is being used to equalise varying channel loss, minimal change in group delay over gain setting will retain good pulse edge information.
An improved output stage provides adequate output current to drive the most demanding loads, says TI. While principally intended to drive ADCs or second-stage amplifiers, the ±60 mA output current will easily drive doubly-terminated 50 Ω lines or a passive post filter stage over the ±1,7 V output voltage range.
For more information contact Les Bidgood, Arrow Altech Distribution, +27 (0)11 923 9600, [email protected]
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