| 摘要 |
An integrating type analog-to-digital converter with improved time measurement capabilities and a very fast conversion cycle. The converter operates by integrating an analog input signal for a predetermined time period and then deintegrating the integrated signal until its output crosses zero. The time it takes for the integrator to cross zero is measured by a digital clock, and the zero crossing is detected as occurring on the first clock pulse after the integrator output has actually crossed zero. The residual output of the integrator at the point of detection is multiplied by a predetermined negative amount and fed back so that the integrator output assumes the multiplied value of the residual. The integrator is then deintegrated for a second time and the time it takes for the integrator output to pass zero is again measured by the clock. The measured time is proportional to the error in the measurement between the detected zero crossing and actual zero crossing in the initial deintegration cycle. By subtracting a predetermined fraction of the second deintegration time from the first deintegration time, a more accurate measure of the actual time it takes the integrator output to cross zero is obtained. By utilizing a plurality of subsequent multiplication and deintegration cycles, the resolution of the actual deintegration time measurement may be further increased. Using this technique, a 12 bit measurement can be made with less than 200 clock pulses as a opposed to 8,192 (213) in prior art converters.
|
