EP-4741983-A1 - TEMPERATURE CORRECTION CIRCUIT FOR A REFERENCE VOLTAGE

EP4741983A1EP 4741983 A1EP4741983 A1EP 4741983A1EP-4741983-A1

Abstract

A temperature correction circuit for a voltage reference circuit includes two amplifiers, each having an output that controls a respective transistor that produces correction current for adjusting the reference voltage. Both amplifiers include one input coupled in a path to a reference voltage source and another input coupled in a path to a temperature sensing diode circuit. One amplifier's output controls the conductivity of its respective transistor to adjust the reference voltage when the temperature exceeds a high temperature set point. The other amplifier's output controls the conductivity of its respective transistor to adjust the reference voltage when the temperature falls below a low temperature set point.

Inventors

PIGOTT, JOHN

Assignees

NXP USA, Inc.

Dates

Publication Date: 20260513
Application Date: 20251030

Claims (15)

A circuit, comprising: a reference voltage source; an output coupled to the reference voltage source, the output for providing a reference voltage; a temperature sensing diode circuit; a first amplifier having a first input coupled in a path to the reference voltage source and a second input coupled in a path to a terminal of the temperature sensing diode circuit; a first transistor including a control terminal coupled to an output of the first amplifier and a first current terminal to provide a correction current for adjusting the reference voltage in response to the temperature sensing diode circuit indicating that a first temperature is being exceeded; a second amplifier including a first input coupled in a path to the reference voltage source and a second input coupled in a path to the terminal of the temperature sensing diode circuit; a second transistor including a control terminal coupled to an output of the second amplifier and a first current terminal for providing a correction current for adjusting the reference voltage in response to the temperature sensing diode circuit indicating that the temperature is below a second temperature.
The circuit of claim 1 wherein a second current terminal of the first amplifier is coupled to the first input of the first amplifier.
The circuit of claim 2 wherein when the temperature sensing diode circuit indicates that the first temperature is being exceeded, the first amplifier drives its output at a voltage to control the conductivity of the first transistor such that the voltage of the first input of the first amplifier matches the voltage of the second input of the first amplifier.
The circuit of any preceding claim wherein the first current terminal of the first transistor provides no correction current for adjusting the reference voltage when the temperature sensing diode circuit indicates that the first temperature is not being exceeded.
The circuit of any preceding claim wherein the first amplifier controls the amount of correction current produced by the first current terminal of the first transistor such that a change the amount of the correction current has a positive correlation with a change in temperature when the first temperature is being exceeded.
The circuit of any preceding claim wherein a second current terminal of the second transistor is coupled to the second input of the second transistor.
The circuit of claim 6 wherein when the temperature sensing diode circuit indicates that the temperature is below the second temperature, the second amplifier drives its output at a voltage to control the conductivity of the second transistor such that the voltage of the second input of the second amplifier matches the voltage of the first input of the second amplifier.
The circuit of any preceding claim wherein the first current terminal of the second transistor provides no correction current for adjusting the reference voltage in response to the temperature sensing diode circuit indicating that the temperature is not below the second temperature.
The circuit of any preceding claim wherein the second amplifier controls the amount of correction current produced by the first current terminal of the second transistor such that a change in the amount of correction current has a positive correlation with a negative change in temperature when the temperature is below the second temperature.
The circuit of any preceding claim wherein the output is provided by a node in an output current path, wherein the correction current provided by the first current terminal of the first amplifier and the correction current provided by the first current terminal of the second amplifier are provided across a resistive circuit of the output current path to adjust the reference voltage.
The circuit of any preceding claim further comprising a resistive path, from the reference voltage source to a power supply rail, wherein the first input of the first amplifier is coupled to a first node of the resistive path and the first input of the second amplifier is coupled to a second node of the resistive path, wherein a resistive circuit is located in the resistive path between the first node and the second node.
The circuit of any preceding claim wherein the terminal of the temperature sensing diode circuit is coupled to the reference voltage source through a biasing current path.
The circuit of claim 12 wherein the second input of the second amplifier is coupled to a node of the biasing current path through at least one resistive circuit.
The circuit of any preceding claim wherein the reference voltage source is characterized as a bandgap voltage source and the reference voltage is characterized as a bandgap reference voltage.
The circuit of any preceding claim wherein the reference voltage source is characterized as a Zener voltage source and the reference voltage is characterized as a Zener reference voltage.

Description

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a temperature correction circuit for a reference voltage. Background A reference voltage is used to provide a stable and predictable voltage in electronic circuits. One type of reference voltage is a bandgap voltage. A bandgap voltage is generated by a bandgap reference circuit and is based on the bandgap of semiconductor devices of the bandgap reference circuit. Another type of reference voltage is a Zener reference voltage. A Zener reference voltage is generated by a Zener reference circuit that includes Zener diode and is based on the breakdown voltage of the Zener diode. For circuits designed to operate over wide temperature ranges, it may be desirable that a reference voltage be relatively constant over the temperature range. Brief Description of the Drawings The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. Figure 1 is a graph showing the voltage over temperature of a prior art bandgap voltage reference circuit.Figure 2 is a circuit diagram of a temperature correction circuit for a voltage reference circuit according to one embodiment of the present invention.Figure 3 is a graph showing the operation of a temperature correction circuit for a voltage reference circuit according to one embodiment of the present invention.Figure 4 is a circuit diagram of a temperature correction circuit for a voltage reference circuit according to one embodiment of the present invention.Figure 5 is a circuit diagram of a temperature correction circuit for a voltage reference circuit according to one embodiment of the present invention.Figure 6 is a circuit diagram of a prior art temperature correction circuit for a bandgap voltage reference circuit. The use of the same reference symbols in different drawings indicates identical items unless otherwise noted. The Figures are not necessarily drawn to scale. DETAILED DESCRIPTION The following sets forth a detailed description of a mode for carrying out the invention. The description is intended to be illustrative of the invention and should not be taken to be limiting. As disclosed herein, a temperature correction circuit for a voltage reference circuit includes two amplifiers, each having an output that controls a respective transistor that produces correction current for adjusting the reference voltage. Both amplifiers include one input coupled in a path to a reference voltage source and another input coupled in a path to a temperature sensing diode circuit. One amplifier's output controls the conductivity of its respective transistor to adjust the reference voltage when the temperature exceeds a high temperature set point. The other amplifier's output controls the conductivity of its respective transistor to adjust the reference voltage when the temperature falls below a low temperature set point. In some embodiments, a resistor divider is implemented in a resistive path and is used to generate temperature set point voltages that are compared with a temperature dependent voltage to generate correction currents at temperatures above a high temperature set point and below a low temperature set point. In some embodiments providing a temperature correction circuit that utilizes two amplifiers and control transistors to provide correction currents may provide for a correction circuit that provides multi temperature segment correction of a reference voltage while utilizing lower accuracy circuits which are less susceptible to variations due to modeling deficiency, package shifts and other imperfections. In addition, the limited gain of the amplifiers may actually "round" the temperature correction to enhance performance in some embodiments. In some embodiments, such a circuit may provide up to a 9X improvement in voltage correction. A reference voltage can be adjusted to have a negligible linear variation over temperature, but may still have a residual quadratic (parabolic) variation over temperature. This parabolic variation may be minimized by adding piecewise linear (PWL) correction that is implemented by generating a correction current dependent on the temperature deviation above a high temperature set point and a correction current dependent on the temperature deviation below a cold temperature set point. Correction current is absent in temperatures between the two set points. Figure 1 is a graph showing a bandgap voltage produced by a prior art bandgap reference circuit across an operating temperature range from -40 C to 160 C. Some bandgap reference circuits are trimmed to cancel linear variation in the bandgap voltage with respect to temperature, leaving an unavoidable 2nd order variation. This 2nd order variation is shown in Figure 1 as a parabolic variation of 5 mV over a temperature range from -40 C to 160 C, from a mid-range peak voltage of 800 mV to 795 mV at