Exposure information quantizing circuit utilizing shift register

Abstract

An exposure information quantizing circuit. A current signal source generates a signal current to be quantized. A controllable bidirectional shift register has a series of bit positions and corresponding signal receiving outputs and is operable to shift a bit sequentially from one position to the next. Each position corresponds to a different divisional range of the signal to be quantized. A unique signal appears only at the output corresponding to the position containing a bit. Means comprises at least one further reference current source responsive to the outputs of the shift register for forming at least a pair of signals corresponding to opposite ends of the divisional range for each output of the shift register. A first logarithmic compression means is coupled to the signal current source for forming a first reference voltage proportional to the logarithm of the signal current. At least one further logarithmic compression means is coupled to the at least one further reference current source for causing the pair of signals to form first and second reference signals proportional to the logarithm of the at least one further reference current source. A voltage comparator forms a direction of shift control signal for the shift register in accordance with comparison thereby of the magnitude of the signal voltage with that of the first and second reference voltages. A source of shift control pulses is provided for the shift register.