Constant-Voltage Circuit Reducing Threshold Voltage Dependence
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Solution Overview
Problem
Existing constant-voltage circuits for mobile communication systems, particularly in linear RF power amplifiers, are heavily dependent on the threshold voltage of field-effect transistors, leading to significant manufacturing variations and instability in the constant voltage supplied.
Innovation Solution
A constant-voltage circuit design that includes first and second field-effect transistors, a bipolar transistor, and a bias circuit, where the power supply is connected to the first node, and a constant voltage is outputted from the source of the first field-effect transistor, with the bias circuit supplying a bias voltage to the bipolar transistor, reducing dependence on the threshold voltage of the field-effect transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant-voltage circuit uses a field-effect transistor Q2 to supply constant voltage Vreg, then the circuit can provide a stable voltage output, but the constant voltage Vreg considerably depends on the threshold voltage Vth of the field-effect transistor Q2, leading to large manufacturing variations
Solution Approach 1:
The patent changes the circuit configuration from directly using the field-effect transistor source voltage to using a voltage divider network with resistors R1 and R2. This parameter change transforms the voltage output equation from Vreg = Vgs2 + Vth to Vreg = (R2/(R1+R2)) * Vdd, eliminating dependence on the threshold voltage parameter Vth and reducing sensitivity to manufacturing variations in transistor characteristics
Solution Approach 2:
The patent introduces resistors R1 and R2 as intermediary elements between the power supply Vdd and the constant voltage output. These resistors form a voltage divider that mediates the voltage transmission, isolating the output from direct dependence on the field-effect transistor's threshold voltage and reducing the impact of manufacturing variations
Data Source
AI summary
A constant-voltage circuit includes: first and second field-effect transistors; a first node connected to the drains of the first and second field-effect transistors; a second node connected to the gates of the first and second field-effect transistors; a bipolar transistor whose collector is connected to the second node; a resistor connected to the source of the second field-effect transistor and the collector of the bipolar transistor; and a bias circuit that is connected to the source of the second field-effect transistor and supplies a bias voltage to the base of the bipolar transistor, wherein a power supply is connected to the first node and a constant voltage is outputted from the source of the first field-effect transistor.