The analog front-end of a proposed BJT-based temperature sensor has been designed. The
design has been analysed using Monte-Carlo simulations with mismatch over all process
corners. The design was implemented in a 90nm generic process design kit. The analog
front-end achieves ultra-low power consumption with a current consumption of 2.3 mA at
a temperature of 27 °C and can operate over the military temperature range of -55 °C -
125 °C. It uses a voltage supply of 2 V.
An adaptive self-biasing operational amplifier was implemented in the bandgap reference
circuit to ensure sufficiently high DC loop-gain. It operates on an ultra-low current consumption
of 631 nA. To reduce errors due to mismatch and process spread two correction
techniques have been employed, that is chopping of the input signals of the operational
amplifier and dynamic element matching of the current sources in the bipolar core.
The residual temperature reading error at the output of the analog front-end is large and
results in significant errors. This is because no compensation technique was implemented
in the analog front-end to compensate for process spread of the BJTs and should be implemented
digitally. The temperature reading errors due to offset and mismatch in the
current sources have been reduced to around 0.03 °C at a temperature of 27 °C. The noise
in the circuit was analysed without the dynamic effects of the DEM because of its simple
implementation and results in an equivalent temperature error of around 0.12 °C, which
indicates the resolution that is achievable. The settling time of the circuit is in the range of
110 ms.