hw.Henan Wang
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Analog design · Voltage references

A precision bandgap voltage reference

Schematic-level design and simulation of an approximately 1.5 V reference, including temperature compensation, startup behavior, and noise analysis.

Purdue SoCET · AMS teamSchematic simulation · No completed layout

A stable on-chip reference

I independently designed and simulated a bandgap reference in Cadence Virtuoso/Spectre as part of Purdue SoCET’s analog and mixed-signal work. The design combines the complementary temperature dependence of VBE and ΔVBE to produce an approximately 1.5 V reference.

The design uses a bandgap core, an amplifier and resistor network, current mirrors, and a startup circuit. The presentation documents the schematic-level implementation and simulation results. There is no completed layout or post-layout result for this project.

Bandgap reference schematic from the project presentation
Schematic implementation from the bandgap presentation. Device and resistor ratios were adjusted for temperature compensation and operating-point behavior.

My contribution

I combined circuit calculations with simulation to choose component ratios and device sizes, establish the intended DC operating point, and examine the reference’s behavior across temperature and startup conditions.

  • Temperature compensation: balancing the PTAT and CTAT contributions through the circuit’s resistor and device ratios.
  • Startup analysis: checking that the reference reaches its operating point, including a slow supply-ramp case.
  • Noise analysis: examining output-noise spectral density and transient-noise behavior in simulation.

Schematic-level results

The nominal temperature sweep gives a reference-voltage range of 1.49835–1.49975 V over −40 to 125 °C, corresponding to an approximate 5.7 ppm/°C temperature coefficient. The presentation also reports about 5.7–7.1 ppm/°C across its evaluated supply/temperature conditions, using supplies of 2.7, 3.0, and 3.3 V.

Nominal bandgap reference temperature sweep with a shallow minimum near the middle of the temperature range
Nominal reference-voltage temperature sweep. The temperature coefficient summarizes the peak-to-peak variation over the specified temperature range.

The startup simulations include repeated power cycles and a 100 µs supply rise time. The reference reaches approximately 1.5 V in the illustrated slow-ramp case. Noise simulations are also included in the original presentation.

Bandgap reference startup waveform for a slow supply ramp
Startup response under a slow power-up ramp, from the project presentation.

Output-noise behavior

Simulated output voltage-noise power spectral density versus frequency
Output-noise power spectral density from the existing design presentation. The spectrum is higher at low frequency and decreases across the plotted range; this remains a schematic-level simulation.

Temperature compensation, startup, and noise probe different aspects of reference behavior. This spectrum adds the frequency-domain check; a band-limited RMS noise value would require integration over a specified bandwidth and is not inferred here.

Design context

The figures on this page are selected schematic-level results from my bandgap presentation.

The presentation acknowledges Seyedehmarzieh Rouhani, Mark C. Johnson, and the Purdue SoCET team.

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