| 摘要 |
A precise digitally-controlled variable attenuation circuit for adjusting the attenuation of a signal in an external circuit includes a signal magnitude detector, a resistance adjustment control, and a resistance divider network. The signal magnitude detector has lower and upper threshold limits representing a desired range of attenuation and is operable to receive and compare a control signal with the lower and upper threshold limits, and, in response thereto, produce either a first signal if the control signal is less than the lower threshold limit or a second signal if the control signal is greater than the upper threshold limit. The adjustment control is capable of receiving the first and second signals and is operable to produce either a digital count-down signal in response to the first signal or a digital count-up signal in response to the second signal. The resistance divider network has a fixed resistance and a digitally-adjustable device with a variable resistance. The fixed resistance is connected between a pair of terminals of an external circuit between which a signal is applied. The variable resistance is connected between one of the terminals of the external circuit and the adjustment control. The digitally-adjustable device will increase or decrease its variable resistance, and thereby correspondingly decrease or increase the attenuation by the divider network of the signal of the external circuit, in response to receiving respectively the digital count-up or count-down signal from the adjustment control.
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