| 摘要 |
<p>A-LAW PCM DECODER An integratable A-law PCM decoder that is relatively insensitive to parasitic and stray capacitance effects and that requires a total capacitance of only 32 times the normalized capacitance Co of the smallest capacitor thereof. The decoder comprises a source of positive and negative reference voltages; a differential input operational amplifier having its non-inverting input connected to ground; a storage capacitor CC=16Co connected as a feedback capacitor between the inverting input and the output terminals of the amplifier so that they operate as a voltage source; binary weighted capacitors C1=Co, C2=2Co, C3=4Co and C4=8Co; and a second unit weighted capacitor C5=Co. Switch means alternately connects one and other sides of C1-C5 (1) between ground and either a characterizations in a PCM coded digital input word for sampling charge, and (2) between one side of CO and ground for transferring charge to CO for the first segment associated with a PCM word, and across CO for redistributing charge on the capacitors for other segments of the designated polarity. The resultant analog signal established on CO in the eighth segment is sampled prior to resetting the charge voltage on CO to substantially zero volts and receipt of the next PCM input word.</p> |
