| 摘要 |
1076955 A/D converters PHILCO-FORD CORPORATION 12 Oct 1965 [12 Oct 1964] 43329/65 Headings H4R and R22X In a vocoder system an input speech signal is applied to sixteen different band-pass filters, the output voltages of these channels being sampled sequentially and digitized by pulse counting using a ramp voltage as a reference, and the invention lies in adjusting the dynamic range of the ramp generator in accordance with the range of voltages from the sixteen frequency channels. The maximum and minimum voltages present on the channels are selected by diode circuits, Figs. 3, 4 (not shown). The maximum voltage is applied to control the charging rate of a capacitor in the ramp generator (and also determines the upper limit of the ramp voltage). A voltage which is a measure of the ratio of the maximum and minimum voltages controls the starting voltage of the ramp generator. This control voltage is derived from an auxiliary quantizer comprising a comparator to which is fed the minimum voltage and which opens a gate to pass pulses to a counter until its two inputs are approximately equal. The other input to the comparator is the maximum voltage attenuated, Fig. 5 (not shown), in accordance with the state of the counter, this attenuated voltage also forming the control voltage. The number of pulses supplied to the counter and the maximum voltage are transmitted to the receiver together with the encoded frequency samples. |
