Voltage to frequency converter with constant current sources

Claim 1

In an integrated circuit for a voltage to frequency converter for converting an analog input signal into a periodic signal having a frequency related to the magnitude of said input signal, a semiconductive substrate, electrical charge integrating means, switching means coupled to said integrating means for sensing predetermined maximum and minimum magnitudes of integrated charge, said switching means including a plurality of transistors integrated in said substrate, said switching means switching from one condition to another in response to said maximum and minimum magnitudes, electrical charge source means coupled to said integrating means including four current sources, one of said sources being responsive to the magnitude of said input signal to produce a first current proportional to said magnitude, said first source being coupled to a second current source having a second current equal to said first curRent, said second source being coupled to both third and fourth current sources which are coupled to said integrating means said third source producing in response to said second current a third current equal to both said first and second currents in a sense to cause the magnitude of the integrating current to increase and said fourth source producing in response to said second current a fourth current twice the magnitude of said first and second currents in an opposite sense to cause the magnitude of integrated current to decrease, said fourth current source producing said fourth current only in response to a predetermined condition of said switching means said charge source means including a plurality of transistors integrated in said substrate and having substantially identical characteristics.