Bias Circuit Using Current Mirror for Stable Bias Voltage
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Solution Overview
Problem
Existing bias circuits that use a resistor instead of a current source to reduce costs face the issue of bias voltage variability with supply voltage changes, leading to unstable bias voltage output.
Innovation Solution
A bias circuit configuration using transistors and resistors, specifically a current mirror circuit and a Widlar bandgap reference circuit, to maintain a stable bias voltage regardless of supply voltage variations by controlling the temperature coefficient of voltage applied to the resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a resistor is used instead of a current source, then cost is reduced, but bias voltage stability deteriorates
Solution Approach 1:
The patent changes the electrical parameters of the circuit by introducing a current mirror configuration with multiple transistors (Q1-Q4) and resistors (R1-R4) to establish a stable reference voltage. The current mirror maintains constant current flow through the resistors, ensuring that the bias voltage remains stable despite supply voltage variations, thus resolving the stability issue while keeping the resistor-based implementation cost-effective
Solution Approach 2:
The patent introduces an intermediary current mirror circuit between the power supply and the bias voltage generation stage. This current mirror acts as a mediator that decouples the bias voltage from supply voltage variations, allowing the use of simple resistors without compromising stability. The current mirror transfers and regulates current to ensure stable operation of the bias circuit
2Adaptability or versatility
If supply voltage varies, then power consumption flexibility is improved, but bias voltage stability deteriorates
Solution Approach 1:
The patent employs parameter changes by utilizing the temperature-dependent characteristics of transistor base-emitter voltages (Vbe) and resistor values. The circuit is designed so that the sum of Vbe voltages and resistor voltage drops maintains a stable bias voltage output. This allows the circuit to adapt to supply voltage variations while maintaining constant bias voltage through careful selection and matching of circuit parameters
Solution Approach 2:
The current mirror configuration provides implicit feedback by automatically adjusting current distribution in response to supply voltage changes. When supply voltage varies, the current mirror detects the change and adjusts the current through the resistors accordingly, ensuring that the bias voltage remains stable. This feedback mechanism enables the circuit to maintain stability across different power consumption conditions
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
The circuit achieves a stable bias voltage output across varying supply voltages, maintaining a fixed bias voltage level despite changes in supply voltage, while also reducing costs by eliminating the need for a current source.
Implementation Method 1
This circuit can produce a fixed bias voltage regardless of temperature variations by using a negative temperature coefficient depending on the transistor structure and a resistor's positive temperature coefficient cancelling each other out
Implementation Method 2
A bias circuit configuration using transistors and resistors, specifically a current mirror circuit and a Widlar bandgap reference circuit
Data Source
AI summary
A bias circuit includes first to sixth transistors and first to fifth resistors. The collector of the fifth transistor is coupled to a node in a path connecting the collector of the fourth transistor and one end of the third resistor. The collector of the sixth transistor Tr6 is coupled to one end of the fifth resistor.