47 Synthesizable Digital Temperature Sensor

47 : Synthesizable Digital Temperature Sensor

Select Project123456789ONSW2
  • Author: Harald Pretl
  • Description: Measure the on-chip temperature and display on the LED display.
  • GitHub repository
  • Clock: 10000 Hz

How it works

By creatively twisting the use of a tristate-inverter (EINVP) a voltage DAC is built. This voltage-mode DAC is used in another twisted arrangement of an EINVP to bias an NMOS into subthreshold operation to discharge a pre-charged capacitor (the input capacitor of an inverter). Since the subthreshold current of a MOSFET is a strong function of temperature, the resulting delay time is also a strong function of temperature, thus a digital temperature sensor is built.

The temperature-dependent digital signal is output at the LED display, showing tens (dot off) and ones (dot on).

A calibration engine via a LUT is included, to allow to linearize and calibrate the shown temperature code.

io_in[0] is used as a CLK signal, and io_in[1] is used a RESET.

io_in[4:2] is used to load and enable the calibration engine.

io_in[7:5] is used to enable various debug modes, presenting internal state signals to the io_out.

How to test

After reset, one temperature measurement is taken per second and displayed using the LEDs. A code ranging 0...63 is displayed with tens first (dot off) and ones later (dot on).

During normal operation io_in[7:5] have to be set to 000. The different debug modes are documented in the Verilog code.

For calibration, the internal LUT can be serially loaded by using CAL_CLK (io_in[2]) and CAL_DAT (io_in[3]). Once fully loaded the calibration engine is enabled by setting CAL_ENA (io_in[4]) to 1 (setting it to 0 displays the raw sensor code).



0clocksegment a (or debug information)
1resetsegment b (or debug information)
2cal_clksegment c (or debug information)
3cal_datsegment d (or debug information)
4cal_enasegment e (or debug information)
5debug_mode[0]segment f (or debug information)
6debug_mode[1]segment g (or debug information)
7debug_mode[2]indicate ones or tens (or debug information)