CMOS Voltage References: An Analytical and Practical Perspective

8

CMOS Voltage Reference without Resistors

In Chapter 5, we reviewed different temperature compensation techniques to design voltage reference circuits. The general technique is of the mutual compensation between weighted PTAT and CTAT sources. The PTAT source and the CTAT source can be in the form of currents or voltages extracted from different thermal characteristics of semiconductor devices. Let’s consider the opamp based β-multiplier bandgap voltage reference circuit which has been thoughtfully analyzed in Chapter 3. The opamp based β-multiplier bandgap voltage reference circuit adopts the basic V_BE − ΔV_BE compensation topology to produce a temperature compensated reference voltage by summing up the V_BE and a weighted ΔV_BE with the factor M as depicted in Equation 3.3. The schematic of the opamp based β-multiplier bandgap voltage reference circuit is shown in Figure 3.4, where ΔV_BE builds on R₁ will be converted to a PTAT current I₂ by performing voltage-to-current conversion with . The PTAT current I₂ is copied from the core circuit to the output circuit by the current mirror formed by M₂ and M₃. The PTAT I₂ is converted back to a PTAT voltage and summed with the CTAT voltage V_BE3 via resistor R₂. This will complete the generation of temperature compensated reference voltage , where ln(N) with N being the ratio of current densities between Q₁ and Q₂. It can be noted that the ...