Operational Amplifier Split-Supply Stages Without Level Shifting
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Solution Overview
Problem
Conventional operational amplifiers require high-voltage transistors for both input and output stages, leading to increased size, parasitic parameters, and power consumption, and necessitate additional level-shift circuits to manage high-voltage control signals, which complicates shutdown and increases costs.
Innovation Solution
Implementing an operational amplifier with different power supply voltages for the input and output stages, using high-voltage transistors in the input stage and low-voltage transistors in the output stage, eliminating the need for a level-shift circuit by powering the input stage with a first power supply voltage and the output stage with a second power supply voltage that is lower, thereby reducing size, cost, and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-voltage transistors are used in both input stage and output stage, then the operational amplifier can handle high common-mode input voltages, but the size of the operational amplifier increases and parasitic parameters increase
Solution Approach 1:
The patent applies different voltage ratings to different stages of the operational amplifier. The input stage uses high-voltage transistors (e.g., 20V rated) to handle high common-mode input voltages, while the output stage uses low-voltage transistors (e.g., 5.5V rated) since it operates at lower voltages. This localized differentiation allows the amplifier to handle high input voltages without requiring all transistors to be high-voltage devices, thereby reducing overall size and parasitic parameters.
2Reliability
If high-voltage transistors are used in the operational amplifier, then the operational voltage threshold is exceeded, but the reliability degrades or the transistor is damaged
Solution Approach 1:
The patent differentiates transistor voltage ratings by stage: high-voltage transistors in the input stage handle high common-mode voltages without degradation, while low-voltage transistors in the output stage operate within their safe voltage thresholds. This staged approach ensures each transistor operates within its reliable voltage range while maintaining overall system adaptability to high input voltages through the input stage's capability.
3Ease of operation
If a level-shift circuit is employed to convert low-voltage control signals to high-voltage control signals, then high-voltage transistors can be shut off, but the size of the operational amplifier increases and cost increases
Solution Approach 1:
The patent eliminates the need for level-shift circuits by using low-voltage transistors in the output stage that can be directly controlled by low-voltage signals. The high-voltage transistors are confined to the input stage where they handle high common-mode voltages but are controlled through the same low-voltage control network. This staged differentiation removes the complexity of level-shifting while maintaining the ability to shut off transistors as needed.
4Ease of operation
If a level-shift circuit is employed in the operational amplifier, then high-voltage control signals can be generated, but power consumption increases because the level-shift circuit continues to function after shutdown
Solution Approach 1:
The patent eliminates power-consuming level-shift circuits by designing the output stage with low-voltage transistors that operate natively at low voltage levels. All control signals remain at low voltage throughout the amplifier, allowing complete shutdown of control circuitry when not in use. The high-voltage capability is localized to the input stage's power handling, not control signals, eliminating continuous power consumption associated with voltage conversion circuits.
5Reliability
If high-voltage transistors are used, then the operational amplifier can operate at high voltages, but the gate-source voltage threshold VGS is less than the required shutdown voltage level
Solution Approach 1:
The patent uses high-voltage transistors only in the input stage where they handle high common-mode voltages, while the output stage uses low-voltage transistors with sufficient VGS thresholds for reliable shutdown control. The control network operates at low voltage and directly controls the low-voltage output stage transistors, ensuring reliable shutdown. The high-voltage input stage transistors are controlled through the same low-voltage network without requiring elevated control voltages.
Data Source
AI summary
An operational amplifier with different power supply voltages includes an input stage and an output stage. The input stage includes a current source for providing a bias current, and a differential input circuit for receiving the bias current and differential input voltage signals, and converting the differential input voltage signal to differential input currents. The input stage is supplied by a first power supply voltage. The output stage includes a load circuit coupled to the differential input voltage signal and for receiving the differential input currents, and outputting a single ended output voltage signal. The output stage is supplied by a second power supply voltage. The second power supply voltage is lower than the first power supply voltage.