A GENERAL CIRCUIT FOR RESISTIVE BRIDGE SENSORS WITH BITSTREAM OUTPUT

A low-offset integrated circuit useful for the readout of the signal c oming from various types of integrated resistive bridge sensors has be en developed in standard bipolar technology, The circuit, using a firs t order Sigma-Delta A/D converter, pro,ides a clock-synchronous pulse rate output which is highly suitable for the communication with a micr oprocessor and for a bus environment. An almost perfect offset cancell ation is achieved by chopping the bridge voltage supply, The simplicit y of the circuit makes it ideal for the integration with the sensors i tself, while the digital interference rejection allows the integration of the digital control circuits for the bus on the same chip, The exp erimental results show that with a clock frequency of 200 kHz a resolu tion of 12 bits is obtained with a conversion time of 20 ms, The remai ning offset is +/-5 mu V. The bridge imbalance can be up to 18 mV/V. D epending on the chosen resolution the input signal bandwidth could be from about 25 Hz (12 bits) up to 400 Hz (8 bits).