Patent ID: 7454967

Claim:
A tire pressure monitoring system comprising a switched capacitor circuit, wherein said switched capacitor circuit comprises: a. a clock, wherein said clock comprises two non-overlapping clock phases that control a state of analog switches of said switched capacitor circuit, whereas said phases comprise phase I and phase II, whereby said switched capacitor circuit operates at frequencies of said clock; b. tire pressure sensor MEMS capacitors, wherein said MEMS capacitors comprise at least one pair of sense capacitors, whereby said sense capacitor pair is measured differentially; c. a capacitance-to-voltage converter, wherein said capacitance to voltage converter is connected to said MEMS sense capacitor; d. a sigma-delta converter, wherein said sigma-delta converter comprises a comparator having a first digital output state and a second digital output state, wherein said first output state comprises a sum of reference voltages and said second output state comprises a difference of said reference voltages, whereas when in said first output state a first capacitor of said MEMS is charged to said first output state on said phase II and a second capacitor of said MEMS is charged to said second output state on said phase I and when in said second output state said first capacitor is charge to said second output state on said phase II and said second capacitor is charged to said first output state on said phase I, whereby an average of said output states is determined and provided to said capacitance-to-voltage converter, whereas an average value of said capacitance-to-voltage converter output is driven to a zero value and a digital output is provided of said average output states that is equal to a difference between said MEMS capacitors divided by their sum multiplied by a ratio of said reference voltages.