A Short Term Analogue Memory

A short term analogue memory is described. It is based on a well-known sample-hold topology in which leakage currents have been minimized partly by circuit design and partly by layout techniques. Measurements on a test chip implemented in a standard 2.4 micron analogue CMOS process show a droop rate of 0.075mV per second with a 1pF hold capacitor. This is equivalent to a retention time of approximately 11/4 minute with 10 bits accuracy, assuming a full scale of +/-3.5V. It is expected that this can be improved by more than an order of magnitude by improving the layout of the hold capacitor. Thus hold times of several hours should be achievable with moderate capacitance values.