| 摘要 |
<p>A charge redistribution circuit for pulse code modulation encoding suitable for use in apparatus for encoding voice in a companded code to maximize signalto-noise performance. The companded code is the fifteen segment approximation of the .mu.255 compression law, wherein each segment contains 16 equal size steps. The circuit includes a single binary weighted capacitor array for the generation of both segment and step boundaries of voice being encoded. Each capacitor in the array has a pair of opposed plates, one plate of each capacitor being commonly coupled together. The circuit further includes a binary comparator having a first input adapted to be coupled to a reference bias potential and a second input coupled to the commonly coupled plates. First switching means connect and disconnect the commonly coupled plates to and from ground potential. Second switching means selectively connect a first common line to an input analog voice signal or to ground potential. Third switching means selectively connect a second common like to a predetermined reference voltage Vref or to a reference voltage Vref/16 (which is 1/16 the predetermined voltage), and selectively couple the first comparator input to ground potential or to the reference bias potential. Fourth switching means, including a switch for each capacitor, selectively couple the other plates of the capacitors to the first or to the second common line. An eight-bit code generator provides a digital eight-bit output upon receipt of a read instruction and control control logic for controlling the four switching means, such logic being responsive to the output of the comparator and providing control signals to the generator. Simultaneously, it causes the third switching means to connect the first comparator input to ground when the sampled input signal lies in the upper four segments and it causes the third switching means to connect the first comparator input to a reference bias potential when the sampled input signal lies in the lower four segments.</p> |
