| 摘要 |
A device for converting analog signal samples into PCM signals, comprising means for successively comparing to a predetermined reference voltage the amplitude of each sample and the successive products thereof by increasing powers of two. At each comparison showing said amplitude of one of said products to be smaller than said reference voltage, a binary digit of a given signalling condition is generated, while a binary digit of the other signalling condition is generated as soon as a comparison shows one of said products to exceed said reference voltage. A remainder signal derived from the latter comparison is transmitted to a linear PCM coder, which delivers a first sequence of PCM signals, while a computer translates the sequence formed by the above-said digits into a second sequence of PCM signals. The assembly of both sequences constitutes the ready-to-be-transmitted PCM signal groups. The device is further characterized in that it makes use, for the successive comparisons, of a plurality of cascaded circuits, each of which includes a difference amplifier with two negative feedback paths, one including a diode having its conduction direction from the output to the input of the amplifier and series connected with a resistance, and the other including a diode having the reverse conduction direction and series-connected with another resistance equal to half or twice the preceding one according to the even or odd rank of the amplifier in the cascade. Thanks to this arrangement, the difference signal resulting from each comparison is multiplied by 1 or 2 according to its polarity, this allowing to use a common reference voltage for all stages of the cascade. |
