| 摘要 |
A variable-transconductance four-quadrant Gilbert-type modulator comprises a differential-transconductance amplifier, a fixed current source, a current sensing resistor, variable-transconductance circuitry, and feedback circuitry. The feedback circuitry is operatively connected to the differential-transconductance amplifier and to the current sensing resistor to receive the modulation voltage signal and to cause the voltage across the current sensing resistor to follow the voltage of the modulation voltage signal thereby causing the differential output current of the differential-transconductance amplifier to be directly proportional to the voltage on its input port thereby improving the linearity of the modulator. Also provided is an isolation output amplifier on the modulated output of the modulator to improve isolation between the carrier input signal and the modulated output.
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