Hong Kong Applied Science and Technology Research Institute Company, Limited

Guangjie Cai

Chun Fai Wong

Tai Yin Wong

Ho Ming (Karen) Wan

Tat Fu Chan

Leung Ling (Alan) Pun

A single-temperature-point temperature-sensitivity sensor assumes that all sensitivity lines converge at absolute zero temperature, so during calibration measurement is needed at only one temperature. A sensor output voltage is generated by current from a mirrored current source flowing through a variable resistor. During calibration, the resistance of the variable resistor and the mirror ratio of the mirrored current source are adjusted. An error amplifier compares voltages generated by unit currents generated by unit current sources to adjust the unit current sources and the mirrored current source. Each unit current flows through a grounded-base PNP transistor. A switchable PNP transistor is in parallel with one of the grounded-base PNP transistors and has its base switched on and off to adjust the PNP current for two measurements. The difference between the two measurements is compared to a calibration target to adjust the variable resistor and mirror ratio during calibration at a single temperature.

Single-temperature-point temperature sensor sensitivity calibration

A low-headroom current driver does not use an op amp or resistor. A sensing transistor having its source connected to a drain of an output transistor senses variations in an output current. The gate, source, and drain voltages of the sensing transistor are mirrored to a sense mirror transistor to control a sense current. The sense current is mirrored to a reference source transistor to generate a mirrored sense current. An error between the mirrored sense current and a fixed reference current is stored as charge on an error-storing capacitor. The stored error charge creates a negative-feedback compensation current that adjusts a gate voltage generated by a feedback-driving transistor. The adjusted gate voltage controls the gate of the output transistor to compensate for the sensed variation in output current. The sensing current is also compensated using a sense-mirror tail transistor connected to the sense mirror transistor.

Low-headroom constant current source for high-current applications

An envelope detector receives an input that is an Amplitude-Modulated (AM) or Amplitude-Shift-Keying (ASK) coded signal. Each channel has a sample switch and a diode that charge an internal sampling capacitor. A hold switch connects the internal sampling capacitor to a summing output capacitor or to a post-processing circuit. A reset switch discharges the internal sampling capacitor after each sample. Two or more channels may be time multiplexed to sample alternate cycles of the input, and then their outputs combined by the summing output capacitor or by the post-processing circuit. The diodes may be reversed to detect the negative envelope rather than the positive envelope. Clocks for the switches may be generated from the input, or may be from a separate clock source. Since the sampling window is open for a whole input cycle, the clock source is insensitive to phase error.

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