Bipolar Clock Level Shifter for Reliable Transistor Turn-Off
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Solution Overview
Problem
Current level shifter circuits used in chopper amplifier applications often fail to effectively turn off transistors due to non-idealities, leading to signal leakage and distortion, especially at high temperatures, as they typically generate unipolar clock signals that do not adequately match the voltage levels required for proper transistor operation.
Innovation Solution
A level shifter circuit is designed to generate bipolar clock signals by using multiple transistor pairs and a clock generation circuit, allowing the clock signals to oscillate between two voltage levels, ensuring effective turn-on and turn-off of transistors by swinging in both polarities relative to the input signal, thereby reducing leakage and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If unipolar clock signals are used in level shifter circuits, then the circuit structure is simple, but transistor turn-off effectiveness deteriorates leading to signal leakage and distortion
Solution Approach 1:
The patent changes the voltage level parameters of the clock signal from unipolar to bipolar, allowing the signal to swing both above and below the input signal level. This parameter change enables the clock signal to properly turn on and off transistors across different voltage domains, resolving the reliability issue while maintaining circuit functionality
Solution Approach 2:
Instead of using a traditional unipolar clock signal that only swings in one direction, the patent inverts the approach by using a bipolar clock signal that swings in both directions relative to the input signal. This inversion allows the clock signal to effectively control transistors in the level shifter circuit by providing both positive and negative voltage swings relative to the input signal level
2Ease of manufacture
If unipolar clock signals are used, then the signal generation is simple, but signal leakage and distortion increase especially at high temperatures
Solution Approach 1:
The patent modifies the clock signal parameters from unipolar to bipolar voltage levels, enabling the signal to swing both above and below the input signal level. This parameter change ensures that transistors are properly turned on and off, significantly reducing signal leakage and distortion even at high temperatures while maintaining manufacturing simplicity
3Ease of operation
If voltage level matching is not implemented, then the circuit operation is simple, but transistor control effectiveness deteriorates
Solution Approach 1:
The patent implements voltage level matching by generating a bipolar clock signal whose voltage levels are specifically tailored to match the requirements of the transistors in the level shifter circuit. The clock signal swings from (Vin - VDD) to (Vin + VDD), ensuring proper transistor control across different voltage domains while maintaining ease of circuit operation
Data Source
AI summary
In some examples, a level shifter circuit comprises: a first transistor pair cascoded at a first input node; a second transistor pair cascoded at a second input node, wherein the first and transistor pairs couple at a first node, a second node, a third node, and a fourth node; a third transistor pair coupled to the first transistor pair at the first and the third nodes, wherein the third transistor pair is configured to generate a first bipolar clock signal; a fourth transistor pair coupled to the second transistor pair at the second and the fourth nodes, wherein the fourth transistor pair is configured to generate a second bipolar clock signal; and a clock generation circuit coupled to the first node, the second node, the third node, and the fourth node.