Analog-to-digital converter system

Claim 1

An analog subsystem of an electronic system which converts the magnitude of an analog voltage into a corresponding digital signal, the electronic system having a digital subsystem for providing a control signal and requiring a timing signal after the control signal, the duration between the control signal and the timing signal being required to be proportional to the magnitude of the analog voltage, the analog subsystem for providing the timing signal including in combination: integrator means; comparator means for providing the timing signal, said comparator means being adapted to be coupled between said integrator means and the digital subsystem; active reference current supply means for providing a reference current at an output terminal which has a constant magnitude and a predetermined direction; active analog voltage-to-current converter means for providing an analog current at an output terminal thereof which has a magnitude that is proportional to the magnitude of the analog voltage, said analog current having a direction opposite to said predetermined direction of said reference current; current steering network means having a first input terminal coupled to said output terminal of said reference current supply means, a second input terminal coupled to said output terminal of said analog voltage-to-current converter means, a control terminal adapted to be coupled to the digital subsystem for receiving the control signal, and an output terminal coupled to said integrator means, said current steering network including four bipolar semiconductor devices connected in a bridge configuration between said terminals of said current steering network and being responsive to the control signal to bypass said reference current while said analog current is coupled to said integrator means and to bypass said analog current while said reference current is applied to said integrator means so that the duration between the control signal and the timing signal is proportional to the magnitude of the analog voltage; reference voltage supply means for providing a constant voltage of a predetermined magnitude at an output terminal thereof; and ramp offset current means coupled between said output terminal of said reference voltage supply means and said second input terminal of said current steering network, said ramp offset current means being responsive to said constant voltage at said output terminal of said reference voltage supply means to provide a constant current at said second terminal of said current steering network which has a magnitude of a predetermined relationship to said magnitude of said reference current for causing the output voltage of said integrator means to change in a predetermined manner even though no analog voltage is applied to said analog voltage-to-converter means, said ramp offset current means further having bias current supply means coupled to said reference voltage supply, current control circuit means having two interconnected transistor means, one of said transistor means being coupled to said second input terminal of said current steering network means and the other of said transistor means being coupled to said bias current supply means, and potentiometer means for adjusting the magnitude of said ramp offset current applied to said second input terminal of said current steering network, said potentiometer means being connected between said two interconnected transistor means.