Abstract
Traditional bandgap reference (BGR) is sensitive to process variation and is not suitable for mass production. Consequently, a stacked piece-wise compensated bandgap reference (SPWBGR) with low beta bipolar is proposed, designed and fabricated in the 0.18 μm high-voltage (HV) BCD process. Two stacked BGR (SBGR) cores make up the proposed BGR circuit. Through setting the target reference voltage near the output voltage of SBGR cores, the feedback resistor ratio is reduced and the base current side-effect is significantly decreased. Notably, the SBGR core is implemented by the low beta npn bipolar and it relaxes the requirement for the high beta bipolar. The two SBGR cores are almost identical except for the temperature slope and feedback ratio. The two cores have different zero temperature coefficient (TC) points, one is set at −5 °C, and the other is set at 60 °C, named as SBGRA and SBGRB, respectively. The SBGRA and SBGRB output the same voltage at their zero TC point. The higher voltage of SBGRA and SBGRB is the output voltage. Through the process of tracking the maximum value of different SBGR cores, the proposed SPWBGR achieves 2.6 ppm/°C TC from −40 to 100 °C. As a result, the average TC for five random samples is 5.3 ppm/°C. The line regulation is 2 mV/V from 4.5 to 5.5 V power supply. The current consumption is 6.8 µA. The active area of the proposed BGR is 0.075 mm2.
Highlights
The precision reference voltage is widely used in mixed-signal and analog circuits in a system on chip (SoC)
A high accuracy reference cannot get from the first-order compensated bandgap reference (BGR) directly, since high precision data acquisition systems need the reference with several ppm/◦ C temperature coefficient (TC)
1536 mV, as the reference voltage for Successive Approximation ADC. (2) stacked piece-wise compensated bandgap reference (SPWBGR) reduces the requirement for high beta npn bipolar by decreasing the feedback resistor ratio, the previous art uses high beta npn to relieve the side effect of the base current
Summary
The precision reference voltage is widely used in mixed-signal and analog circuits in a system on chip (SoC). Another piece-wise compensation utilizes the exponential compensation in the temperature range and logarithmic compensation in the high temperature range [6] Another method utilizes two identical first-order bandgaps with different zero temperature points [7]. In order to avoid the multi-point temperature calibration for cost saving, and obtain a precision output voltage, a stacked piece-wise compensated BGR (SPWBGR) is introduced. By setting a small feedback resistor ratio, the offset voltage of the proposed SPWBGR is small, and the side-effect of the base current on TC is ignorable, while the high beta of the npn bipolar is not critical anymore. (2) SPWBGR reduces the requirement for high beta npn bipolar by decreasing the feedback resistor ratio, the previous art uses high beta npn to relieve the side effect of the base current. The offset voltage is amplified by a large feedback resistor ratio. (4) Current consumption of the two stages of SBGR decreases by removing the bias branch that generates the cascode bias. (5) The layout area is significantly reduced by optimizing the device size
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