this point either capacitor c x or c r is allowed to begin charging again waveform 382 in fig1 illustrates the operation of the fig9 circuit by showing the output voltage vout on line 368 as shown in fig1 the time period t x between t1 and t2 represents the interval during which the transducer capacitor c x is being repetitively charged and discharged by circuit 256 similarly the time period t r between times t0 and t1 represents the interval of time during which the circuit 256 is charging and discharging the reference capacitor c r during the time period t off from times t2 to t4 the circuit 256 shown in fig9 is disabled thus allowing the voltage vout on line 368 to approach the value of voltage vdd on line 266 as shown by waveform portion 384 of waveform 382 in fig1 since the constant source 366 may be measured or otherwise calibrated at a known temperature any change in the rate of charging of reference capacitor c r can be correlated with reasonable accuracy to changes in temperature of the integrated circuit chip 336 in which capacitor c r is located given the small size of the sensor 30 and the proximity of capacitor c r to the diaphragm 130 it will be appreciated that c r provides a convenient and accurate method for determining the temperature of the pressure transducer of sensor 30 so that.