Analog circuit for an analog-to-digital converter of the dual-slope integrating type

Claim 2

In an analog-to-digital conversion system, an amplifier of relatively high gain having signal inverting and signal noninverting input terminals and an output terminal, means for applying an analog signal to the noninverting input continuously during a conversion cycle comprised of successive first and second time intervals of which the first time interval is of fixed duration, a capacitor coupling the amplifier output to the signal inverting input and charging at a rate which is a function of the magnitude of the analog signal applied to said noninverting input during the first time interval, a source of reference current and switch means coupled to said source of current and operable to selectively apply the reference current to said inverting input in a direction to withdraw signal from said capacitor at a substantially constant rate, means for timing the operation of said switch means, means coupled to the timing means for providing a digital representation of the analog signal magnitude, a constant potential source, a plurality of resistors, each resistor having two ends with one end thereof connected to said constant potential source, and a switch for selectively connecting the other ends of said resistors to said inverting terminal, said resistors having different resistance values referenced to different full scale ranges of analog signal magnitude.

Claim 3

In an analog-to-digital conversion system, a high gain amplifier D.C. having signal inverting and signal noninverting input terminals and an output terminal, means for applying an analog current to the noninverting input continuously during a conversion cycle comprised of successive first and second time intervals of which the first time interval is of fixed duration, a capacitor coupling the amplifier output to the signal inverting input and charging at a rate proportional to the magnitude of the analog current applied to said noninverting input during the first time interval, a source of reference current having a magnitude greater than the corresponding full scale magnitude of analog current and poled in a direction to discharge said capacitor, switch means coupled to said source of current and operable to selectively apply the reference current to said inverting input in a direction to discharge said capacitor at a substantially constant rate which is also a function of the applied analog current magnitude, means for timing the operation of said switch, means coupled to the timing means for providing a digital representation of the analog signal magnitude, a constant potential source, a plurality of range-determining resistors, each resistor having two ends with one end thereof connected to said constant potential source, said resistors having different resistance values referenced to different desired full scale ranges of analog current and a range-changing switch for selectively connecting different ones of the other ends of said resistors to said inverting terminal to change the measuring range of said system.

Claim 4

In an analog-to-digital conversion system, a high gain amplifier D.C. having signal inverting and signal noninverting input terminals and an output terminal, means for applying an analog current to the noninverting input continuously during a conversion cycle comprised of successive first and second time intervals of which the first time interval is of fixed duration, a capacitor coupling the amplifier output to the signal inverting input and charging at a rate proportional to the magnitude of the analog current applied to said noninverting input during the first time interval, a source of reference current having a magnitude greater than the corresponding full scale magnitude of analog current and poled in a direction to discharge said capacitor, switch means coupled to said source of current and operable to selectively apply the reference current to said inverting input in a direction to discharge said capacitor at a substantially constant rate which is also a function of the applied analog current magnitude, means for timing the operation of said switch, means coupled to the timing means for providing a digital representation of the analog signal magnitude, a constant potential source, a plurality of range-determining resistors, each resistor having two ends with one end thereof connected to said constant potential source, said resistors having different resistance values referenced to different desired full scale ranges of analog current and a range-changing switch for selectively connecting different ones of the other ends of said resistors to said inverting terminal to change the measuring range of said system.

Claim 5

The system as claimed in claim 2 wherein the potential level of said constant potential source is lower than the normal voltage at said one end of each resistor.

Claim 6

The system as claimed in claim 3 wherein said potential level is zero volts.

Claim 7

The system as claimed in claim 2 wherein said constant potential source is ground.