CMOS Push-Pull Amplifier Bias Control via Bulk Voltage Feedback
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Solution Overview
Problem
CMOS push-pull amplifiers face challenges in maintaining consistent bias current due to small variations in supply voltage, leading to unpredictable power consumption and variations in input and output impedances, gain, and noise characteristics.
Innovation Solution
A control circuit measures current or voltage parameters indicative of bias current and adjusts the bulk voltage of transistors to maintain a target bias current level, thereby controlling threshold voltages and stabilizing power consumption and signal characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If two transistors are connected in series between positive and negative voltage supply terminals, then the circuit can function as a CMOS push-pull amplifier, but small variations in supply voltage cause large variations in bias current
Solution Approach 1:
The patent implements a feedback mechanism where the bulk voltage of at least one transistor is adjusted based on measured bias current or voltage parameters. The control circuit continuously monitors the bias current and dynamically modifies the bulk voltage to compensate for supply voltage variations, thereby maintaining stable bias current operation.
Solution Approach 2:
The patent changes the bulk voltage parameter of the transistor to control and stabilize the bias current. By varying the bulk voltage in response to measured parameters, the system compensates for supply voltage fluctuations and maintains consistent amplifier performance.
2Adaptability or versatility
If supply voltage varies, then the amplifier can adapt to different power conditions, but power consumption becomes unpredictable and difficult to control
Solution Approach 1:
The control circuit uses feedback from measured voltage or current parameters to dynamically adjust the bulk voltage, ensuring that power consumption remains predictable despite supply voltage variations. This closed-loop control allows the amplifier to adapt to different power conditions while maintaining consistent energy usage characteristics.
3Adaptability or versatility
If supply voltage varies, then the amplifier can operate under different conditions, but input and output impedances, gain, and noise characteristics vary
Solution Approach 1:
The patent employs feedback control where the bulk voltage is continuously adjusted based on measured parameters to maintain consistent input and output impedances, gain, and noise characteristics. This ensures reliable signal processing performance across varying operating conditions.
Solution Approach 2:
By dynamically changing the bulk voltage parameter in response to measured circuit parameters, the system compensates for supply voltage variations and maintains consistent signal characteristics, including impedances, gain, and noise properties.
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 approach ensures predictable power consumption and improved consistency in input and output impedances, gain, and noise characteristics by maintaining a steady bias current, even with variations in supply voltage.
Implementation Method 1
The modification of the at least one transistors bulk voltage is used to control the at least one transistors threshold voltage, and the at least one transistors threshold voltage has a direct effect on the level of the bias current.
Data Source
Figure 1~2
Figure 3~4a
Figure 4b~5
AI summary
There is provided a method and apparatus for maintaining a bias current (IBIASI) that flows through two transistors (MN2, MP2) at a target level. The two transistors are both connected to form a series network between positive (VDD) and negative (GND) voltage supply terminals. The bias current flows through the two transistors (MN2, MP2) when the circuit is at equilibrium, and the threshold voltage of the transistors is controlled by controlling the voltage (VBI, VB2) that is applied to the transistors bulk terminals. In addition to the two transistors, there is provided a control circuit (25) that measures a circuit parameter (VDD) 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 (VBI, VB2) SO as to alter the transistors threshold voltages and maintain the level of bias current at a target level.