| 摘要 |
Disclosed is a control circuit which provides a control signal to a control terminal of a voltage controlled amplifier (VCA), such as a SSM-2018 VCA manufactured by Analog Devices, such that a signal input to the VCA is amplified between +12 dB gain and full attenuation. The VCA is characterized by a predetermined control attenuation relationship which determines the gain of the input signal. The control circuit includes: a DC voltage source, preferably a linear potentiometer, which provides a voltage in a fixed range; an operational amplifier for rescaling the fixed range of voltages to a second range; a pair of curve-shaping circuits which adjust the second range; and a circuit, including an amplifier circuit, a voltage divider and a zener diode, which adds a DC offset and adapts the signal from the DC voltage source to a range of voltages calculated from the control attenuation relationship. This circuitry permits faster adjustment of the control signal over ranges resulting in full attenuation or +12 dB gain without significant increase in noise and distortion in the signal output from the VCA.
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