Pseudoanalogue operation in digital circuits

Components such as amplifiers and analogue-digital convertors are not usually available as part of a standard digital gate array system. A technique is presented by which low-level analogue input signals can be amplified and converted into a digital representation using only the digital cells on a standard gate array in conjunction with a few external passive components. An analysis of the basic method of negative feedback around a clocked flip-flop is presented, which demonstrates that a pseudoanalogue amplifier device can be produced whose gain and zero offset are controllable to within 1% or better by the passive components. This device is then developed into an A/D convertor with a typical 8 bit accuracy and 10 mu s conversion time.