Cascode Current Mirror Circuit for Low Voltage Accuracy
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Solution Overview
Problem
Existing reference voltage generating circuits face challenges in achieving high current mirror accuracy at low power supply voltages, leading to decreased accuracy and power supply rejection ratio, particularly when using current mirror circuits with p-channel transistors, which are unable to operate effectively below a certain voltage threshold.
Innovation Solution
The implementation of a cascode current mirror circuit with a specific configuration that includes multiple p-channel transistors connected in a manner that allows for high current mirror accuracy at low power supply voltages, utilizing a differential amplifier and multiple current-voltage converter circuits to generate a reference current with minimal temperature coefficient, and converting this current into a reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a current mirror circuit with p-channel transistors is used in a reference voltage generating circuit, then the circuit can generate reference voltage, but the current mirror accuracy decreases and power supply rejection ratio deteriorates when operating at low power supply voltages
Solution Approach 1:
The current mirror circuit is divided into multiple stages with intermediate voltage generation. The circuit segments the voltage requirement by generating an intermediate voltage (Vb) that is applied to gates of transistors in series, allowing each transistor to operate at lower individual voltage drops while maintaining overall functionality at low power supply voltages
Solution Approach 2:
An intermediate voltage generation circuit is introduced as a mediator between the power supply and the current mirror transistors. This intermediary circuit generates the necessary gate voltages to ensure proper transistor operation and maintain current mirror accuracy even when the overall power supply voltage is low
2Power
If a current mirror circuit with p-channel transistors is used in a reference voltage generating circuit, then the circuit can generate reference voltage, but the power supply rejection ratio decreases when operating at low power supply voltages
Solution Approach 1:
The power supply voltage is segmented into multiple voltage drops across series-connected transistors, with intermediate voltage generation providing stable reference points. This segmentation isolates the current mirror from direct power supply variations, improving rejection ratio while enabling low voltage operation
Solution Approach 2:
The intermediate voltage generation circuit acts as a buffer and mediator that decouples the current mirror circuit from power supply fluctuations. By providing stable gate voltages through this intermediary stage, the circuit achieves high power supply rejection ratio even at low operating voltages
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables a reference current generating circuit with high accuracy and the ability to operate at low power supply voltages, improving the accuracy of reference voltage generation and temperature detection circuits while maintaining high power supply rejection ratio.
Implementation Method 1
Channel length modulation effect of a transistor included in an integrated circuit appears as the rules of process of the integrated circuit become fine. This leads directly to a decrease in the current mirror accuracy of the current mirror circuit
Implementation Method 2
currents that are equal to each other are supplied to the current mirror circuit. Thus, a current obtained by a forward voltage of a diode having a negative temperature coefficient and a current obtained by a voltage difference between two diodes having a positive temperature coefficient are added, so that a reference current with a small temperature coefficient is generated
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3C
AI summary
A reference current generating circuit with high current mirror accuracy is provided by low power supply voltage operation. The reference current generating circuit includes a cascode current mirror circuit 1 outputting mirror currents I 1 and I2, and a reference current Iref, a current-voltage converter circuit 2 converting the mirror current I1 into a voltage V1, a current-voltage converter circuit 3 converting the mirror current I2 into a voltage V2, a differential amplifier 4 in which the voltage V1 is input to a first input terminal and the voltage V2 is input to a second input terminal, a voltage-current converter circuit 5 converting a voltage V3 output from the differential amplifier 4 into currents I3 and I4, and a current-voltage converter circuit 6 converting the current I3 into a voltage V4 which is output to a gate of a transistor in the cascode current mirror circuit.