Patent ID: 7352166
Filing Date: 2008-04-01
Classification: G01R

Abstract:
1. A method for sampling and digitizing a resistance ratio measurement from an impedance-varying input sensor, comprising: connecting said input sensor and a reference resistor in series between a first node and a second node; applying a DC excitation current from a high impedance current source to said input sensor and said reference resistor; sampling the voltage across said input sensor using a first pair of switches, said first pair of switches being controlled by complementary signals so that only one switch of the first pair of switches is closed at a time; generating an input voltage step having a magnitude corresponding to said voltage across said input sensor by the switching action of said first pair of switches, said input voltage step being indicative of the resistance of said input sensor; sampling the voltage across said reference resistor using a second pair of switches, said second pair of switches being controlled by complementary signals so that only one switch of the second pair of switches is closed at a time; generating a reference voltage step having a magnitude corresponding to said voltage across said reference resistor by the switching action of said second pair of switches, said reference voltage step being indicative of the resistance of said reference resistor; coupling said input voltage step to an integrator; integrating charges corresponding to a transition of said input voltage step on an accumulation capacitor; coupling said reference voltage step to said integrator; generating a data dependent signal for deactivating or activating said integrator; integrating charges associated with a transition of said reference voltage step when said data dependent signal has a first value or disregarding charges associated with the transition of said reference voltage step when said data dependent signal has a second value, said transition of said reference voltage step being opposite to said transition of said input voltage step; comparing a signal corresponding to said charges accumulated on said accumulation capacitor with a reference level; and generating an output signal as a result of said comparing, said data dependent signal having said first value and said second value corresponding to respective logical levels of said output signal, wherein after a plurality of sampling cycles, said output signal forms a digital data stream having an ones density proportional to a ratio of the resistance of said input sensor to said reference resistor.