Push-Pull Amplifier Bias Control Using Transistor Bulk Voltage
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Solution Overview
Problem
CMOS push-pull amplifiers with two transistors connected in series between voltage supply terminals face challenges in maintaining consistent bias current due to small variations in supply voltage, leading to unpredictable power consumption and variations in input/output impedances and noise characteristics.
Innovation Solution
A control circuit measures a parameter indicative of the bias current and adjusts the bulk voltage of at least one transistor to maintain a target bias current level, thereby controlling the threshold voltage and stabilizing power consumption and noise characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two transistors are connected in series between voltage supply terminals to form a CMOS push-pull amplifier, then the amplifier can provide low-noise wideband amplification, but small variations in supply voltage cause large variations in bias current leading to unpredictable power consumption and variations in input/output impedances and gain
Solution Approach 1:
The patent implements a feedback mechanism where a control circuit continuously monitors the bias current flowing through the series-connected transistors and dynamically adjusts the bulk voltage of at least one transistor to maintain the bias current at a target level. This closed-loop feedback system compensates for supply voltage variations, ensuring consistent power consumption and stable amplifier operation throughout the patent's operation
Solution Approach 2:
The patent changes the bulk voltage parameter of the transistor to control and stabilize the bias current. By dynamically adjusting the bulk voltage in response to measured bias current levels, the system maintains consistent power consumption and amplifier characteristics despite variations in supply voltage, as described throughout the patent
2Device complexity
If the bias current is allowed to vary with supply voltage, then the circuit design is simpler, but the input and output impedances, gain, and noise characteristics vary making consistent operation difficult to achieve
Solution Approach 1:
The control circuit employs feedback to continuously monitor bias current and adjust bulk voltage accordingly, maintaining stable amplifier characteristics. This feedback mechanism ensures consistent input/output impedances, gain, and noise characteristics by compensating for supply voltage variations in real-time, as throughout the patent
Solution Approach 2:
The patent dynamically changes the bulk voltage parameter to maintain constant bias current, thereby stabilizing all amplifier characteristics including input/output impedances, gain, and noise properties. This parameter adjustment approach enables consistent operation without requiring complete redesign of the amplifier topology
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 solution ensures predictable power consumption and consistent noise characteristics by maintaining a steady bias current, improving the amplifier's performance and preventing supply voltage variations from affecting the signal path.
Implementation Method 1
alter the bulk voltage of at least one of the transistors so as to maintain the bias current at a target level. The modification of the at least one transistors bulk voltage is used to control the at least one transistors threshold voltage
Data Source
AI summary
There is provided a method and apparatus for maintaining a bias current that flows through two transistors at a target level. The two transistors are both connected to form a series network between positive and negative voltage supply terminals. The bias current flows through the two transistors when the circuit is at equilibrium, and the threshold voltage of the transistors is controlled by controlling the voltage that is applied to the transistors bulk terminals. In addition to the two transistors, there is provided a control circuit that measures a circuit parameter that is indicative of the level of bias current flowing through the two transistors. In response to the measured parameter, the control circuit adjusts the bulk voltage levels of the two transistors so as to alter the transistors threshold voltages and maintain the level of bias current at a target level.