| 摘要 |
This invention relates to the amplification circuitry, storage circuitry and encoding circuitry of a feedback comparison type PCM encoder. This circuitry incorporating a storage capacitor operates sequential on each analog signal sample of a plurality of such samples applied thereto in a TDM channel format. A balanced circuit arrangement incorporating differential amplifiers is employed for each of the above mentioned components of the PCM encoder. The capacitor is fed from the TDM input through a first gated differential amplifier. Then this amplifier is blocked by a second differential amplifier behaving as a variable impedance. The blocking of the first differential amplifier prevents leakage from the TDM input to a third differential amplifier which includes the storage capacitor. The charge of the capacitor, corresponding to the previous sample, is adjusted to each new sample at a constant current rate. Under this condition one capacitor terminal jumps towards the new potential impressed on that terminal and the other capacitor terminal moves linearly towards the new potential on the other terminal. A fourth differential amplifier is coupled across the capacitor and the output currents thereof are algebraically combined with the input currents derived from the previously coded sample by a digital-to-analog converter present in the feedback path of the encoder. The results of the algebraic addition of the two currents are provided as a balanced voltage input to a binary voltage comparator which provides the code representing the magnitude of the present sample.
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