Low cost heating regulation circuit for self-heating flow mems

A flow sensor device comprising:

• a substrate;
• a membrane suspended by the substrate;
• an upstream resistive element situated on the membrane having a first temperature coefficient of resistance (TCR);
• a downstream resistive element situated on the membrane adjacent the upstream resistive element having a second TCR, wherein the first TCR and the second TCR are substantially the same, with no intervening heater element positioned between the upstream resistive element and the downstream resistive element;
• a first upstream node coupled to a first end of the upstream resistive element and a second upstream node coupled to a second end of the upstream resistive element;
• a first downstream node coupled to a first end of the downstream resistive element and a second downstream node coupled to a second end of the downstream resistive element;
• and
• a low TCR resistor coupled to one of the upstream resistive element and the downstream resistive element having a third TCR where the third TCR is at least an order of magnitude less than the first TCR and is at least an order of magnitude less than the second TCR;
• wherein the upstream resistive element has an electrical resistance between the first upstream node and the second upstream node and the downstream resistive element has an electrical resistance between the first downstream node and the second downstream node;
• and
• wherein the resistance of the upstream resistive element is within 20 percent or less of the resistance of the downstream resistive element when the upstream resistive element is at the same temperature as the downstream resistive element.

A micromechanicalelectrical system (MEMS) flow sensor die comprising:

• a substrate, wherein the substrate is 1 square millimeter or less in planar area;
• a membrane suspended by the substrate;
• an upstream resistive element situated on the membrane;
• a downstream resistive element situated on the membrane adjacent the upstream resistive element, with no intervening heater element positioned between the upstream resistive element and the downstream resistive element.