An Embedded Charge Pump for a Zener-Based Voltage Reference Compensated Using a ∆VBE Stack

V. Bucur, G. Banarie (Analog Devices Inc., Ireland), S. Marinca, M. Bodea (Univ. Politehnica of Bucharest, Romania)

Two temperature insensitive voltage reference types are widely used today: buried Zener and bandgap voltage. Reference voltages based on buried Zener diodes are less sensitive to stress and have lower Long Term Drift (LTD) (approx. 3ppm/1kh), but require minimum supply voltage, of at least 6.5V. Bandgap-type voltage references can operate off supply voltages as low as 1V, but they have larger LTD compared to Buried Zener type (typically <30ppm/1kh). An enhancement to the “Low Drift Zener-Based Voltage Reference” resented in [1] is discussed in this paper. Reducing the voltage supply requirements from 6.5V to 3.3V by means of a Charge Pump (CP) and mitigating the shortcomings of the CP, specifically in the form of enhanced ripple reduction architecture techniques is presented in detail. Total ripple attenuation from the CP voltage output to the voltage reference output exceeds 125dB. As shown in simulation, the proposed CP circuit offers good pumping gain, simplicity and a small IC footprint of 0.75mm2. A test chip (Fig. 2.) according to the discussed specifications and features is due for tapeout.