CMOS Voltage References: An Analytical and Practical Perspective

5

Temperature Compensation Techniques

The fundamental circuit topology to remedy the temperature dependency of the voltage reference circuit is the mutual compensation between the PTAT and CTAT voltage/current sources. These temperature dependent factors can be constructed in either voltage or current forms. In either case, the temperature compensated voltage reference circuit can be considered to consist of three sub-circuits. The first sub-circuit generates the PTAT voltage/current, while the second sub-circuit generates the CTAT voltage/current. The two temperature dependent voltages/currents are summed by the third sub-circuit, which will also provide the I-V conversion. As an example, the third sub-circuit of the opamp based β-multiplier bandgap voltage reference circuit in Chapter 3 performs the summing operation by means of converting the PTAT current to voltage using a resistor, and then the PTAT voltage is super-positioned on top of a CTAT voltage to generate a temperature compensated reference voltage. There are a large number of circuit topologies to perform the summation operation and each has its own pros and cons. Similarly, there are a large number of circuit topologies to generate the PTAT and CTAT voltages/currents. Furthermore, depending on their availability in the fabrication process, different electron devices are employed in each topology to generate stable CTAT and PTAT voltages and currents. Previous chapters discussed the application of the base-emitter ...