| 摘要 |
<p>In a Pulse Code Modulated (PCM) circuit chip, apparatus in the transmit path to compensate for an offset voltage signal from a band-pass filter includes an up-down counter which is actuated to provide a digital value equivalent to the offset signal and a digital to analog converter coupled to the counter to provide an analog signal representing the digital value in the counter. During an initialization phase, the counter is incremented until the digital value of the counter provides, by means of the digital to analog converter, an analog signal that compensates for the off-set signal. After the initialization phase when the band-pass filter's offset voltage is compensated, then other circuitry including an exclusive OR gate and an associated overflow counter are used to eneable or disable the up-down counter to insure that the PCM output signal is an accurate representation of the analog input signal. The up-down counter, during the operation phase following the initialization phase, is only enabled when the analog input signal is not present.</p> |
