A design and implement of impedance spectrum measurement system controlled by a single-chip microprocessor is described.The synchronous orthogonal signals are obtained by using direct digital synthesis（DDS）.The impedance is converted to voltage based on the dual-differential subtraction.The affections of noise can be reduced significantly by using the dual lock-in amplifiers.Due to gain of the measurement channel changes with frequency

so the calibration is used.The programmable switched-capacitor low pass filters are used to speed up measurement.The simulation experimental results show covering frequency range is 1 Hz

1

00 kHz and SNR is-10 dB

1

0 dB with Gauss white noise

measurement relative error is less than 4 %.