| 摘要 |
Multi-channel impedance cardiograph comprises a sine generator, a multiplexer, a high-pass filter, an amplifier, an analogue-code converter and a microcontroller. A compensation circuit reduces the required order of the analogue-code converter. The compensation circuit comprises a second sine signal generator, an adder, a comparator for comparing its input signal with a reference signal, and a counter. Both sine signal generators are synchronised and the signal from the body is compensated by the signal of the second sine signal to normalize the input signal of the analogue-code converter. The first sine signal generator and the counter are started simultaneously. The counter stops when the comparator's output reverses polarity. The phase shift between the signals of first and second sine signal generators is calculated from the counter content. The amplitude of the compensation signal generator is adjusted so that the output code of the analogue code converter is within working range. |
