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Method for very low-voltage bandgap reference and temperature sensor circuits

IP.com Disclosure Number: IPCOM000125132D
Publication Date: 2005-May-19
Document File: 6 page(s) / 100K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for very low-voltage bandgap reference and temperature sensor circuits. Benefits include improved functionality and improved performance.

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Method for very low-voltage bandgap reference and temperature sensor circuits

Disclosed is a method for very low-voltage bandgap reference and temperature sensor circuits. Benefits include improved functionality and improved performance.

Background

              Conventional bandgap reference circuits produce output only at a fixed bandgap voltage of approximately 1.2V. Although modified circuits provide scalable output that can be lower than 1.2V, PMOS transistor current mirrors can vary due to process mismatch and output error.

              An accurate reference voltage signal is required for many analog circuits, such as data converters and power supply circuits. As the integration of radio frequency (RF) and analog circuits continues in smaller CMOS technologies, less sensitive circuits for reference generation are required.

              In the conventional bandgap circuit, anode side nodes of bandgap core are sensed by an operational amplifier (op-amp). The voltage on the other side of the two resistors, R1 and R2, is forced so that feedback equalizes the voltage of the two sense nodes. In general, the sense node and the force node do not have to be on the anode side and resistor end, as long as the following conditions are met:

•             Feedback is negative.

•             Voltage across the core branches are equal.

•             Current through the two diodes are equal.

General description

              The disclosed method is very low-voltage bandgap reference and temperature sensor circuits. They generate output voltage lower than conventional designs. The same circuits can be used as temperature sensors because the buffered output node has an inherent negative temperature coefficient.

              The major advantage of the disclosed method is that it depends only on current matching between passive resistors, which reduces the circuits’ sensitivity.

Advantages

              The disclosed method provides advantages, including:
•             Improved functionality due to providing four very low-voltage bandgap reference and temperature sensor circuits
•             Improved performance due to providing stable circuits by reducing the circuits’ sensitivity

Detailed description

                            The disclosed method includes four configurations of bandgap reference circuits that generate output voltage lower then conventional designs. Additionally, the circuits function as temperature sensor circuits.

              By changing the sense node and force node configurations, a temperature-independent low-voltage reference signal can be generated.

              Offset sensitivity is defined as the ratio variation of absolute value of Vref when a 0.1-mV offset occurs in the op-amp.

Circuit 1

              The sense node for this circuit is comprised of the cathode-side nodes of the bandgap core. The anode-side nodes are connected as a force node. The polarity of the differential op-amp is reversed compared to a conventional bandgap due to direct voltage fe...