Patent ID: 7387022

Claim:
A thermal mass flow transducer, comprising: first and second constant current sources each operable to supply a constant current; a first temperature sensitive element coupled to receive the constant current supplied from the first constant current source and configured, upon receipt thereof, to generate a first temperature signal representative of its temperature; a second temperature sensitive element coupled to receive the constant current supplied from the second constant current source and configured, upon receipt thereof, to generate a second temperature signal representative of its temperature; a heater element in thermal communication with the first temperature sensitive element and thermally isolated from the second temperature sensitive element, the heater element coupled to receive a heater current and, in response thereto, to generate heat; and a control circuit coupled to the heater element and further coupled to receive the first and second temperature signals, the control circuit operable, in response to the first and second temperature signals, to: (i) determine a temperature difference between at least the first and second temperature sensitive elements, (ii) generate a pulse width modulation (PWM) current based on the determined temperature difference, and (iii) supply the heater current to the heater element at a current magnitude sufficient to maintain the temperature difference at a predetermined value.