| 摘要 |
An electronic impedance device provides a variable impedance in, for example, a Dolby noise reduction system. The device includes an input terminal connected to a source of a signal voltage. A differential voltage-to-current converter circuit, having a relatively high input impedance, converts the input signal voltage into two differential output currents that are variable with the input signal voltage. A pair of p-n junction elements, such as diodes, are connected to the converter circuit via a current transfer circuit. The current transfer circuit transfers the differential output currents to the p-n junction elements. A differential current amplifier circuit is responsive to the voltage built up across the p-n junction elements. The differential current amplifier has an output terminal to produce an output current. A feedback line connects the output terminal of the amplifier circuit to the input terminal for permitting the output current of the amplifier circuit to be fed back to the input terminal of the device.
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