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Thermocouple Temperature Measurement System with Less Than 500 ОјA Current Drain (CN0206)

The circuit shown in Figure 1 is a complete thermocouple system based on theAD7793 24-bit sigma-delta (Σ-Δ) analog-to-digital converter (ADC). The AD7793 is a low power, low noise, complete analog front end for high precision measurement applications. The device includes a programmable gain amplifier (PGA), an internal reference, an internal clock, and excitation currents, thereby greatly simplifying the thermocouple system design.

The AD7793 consumes only 500 μA maximum, making it suitable for any low power application, such as smart transmitters where the complete transmitter must consume less than 4 mA. The AD7793 has a power-down option. In this mode, the complete ADC, along with its auxiliary functions, is powered down so that the part consumes 1 μA maximum.

Because the AD7793 provides an integrated solution for thermocouple design, it interfaces directly to the thermocouple. For the cold junction compensation, a thermistor along with a precision resistor is used. These are the only external components required for the cold junction measurement other than some simple RC filters for EMC considerations.

Figure 1. Thermocouple Measurement System with Cold Junction Compensation (Simplified Schematic: All Connections and Decoupling Not Shown)


  • Typical temperature range of -200 C to +400 C
  • T-type thermocouple measurement system
  • Low power 500uA max, and low system noise of 0.2 degrees
  • Single chip solution with programmable gain and cold junction compensation
  • High performance and accuracy


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