Differential Amplifier Circuit With Depletion NMOS Rail-to-Rail Stability
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Solution Overview
Problem
Conventional differential amplifier circuits used in liquid crystal display panels experience significant amplitude difference deviation in voltage ranges near the power supply voltage VDD or ground voltage VSS, due to switching in circuit operations, which is not adequately addressed by existing configurations using both NMOS and PMOS transistor pairs or solely depletion-type NMOS transistor pairs.
Innovation Solution
A differential amplifier circuit configuration that includes an NMOS transistor pair and a PMOS transistor pair, with the NMOS transistors being non-doped type, formed on a P-type substrate without a P well, and a folded cascode type current mirror, ensuring operation across the entire voltage range without switching and reducing amplitude difference deviation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If both NMOS transistor pair and PMOS transistor pair are used in the differential amplifier circuit, then the Rail-to-Rail operation is achieved, but the amplitude difference deviation is aggravated in voltage ranges near power supply voltage or ground voltage
Solution Approach 1:
The patent changes the type of NMOS transistor from enhancement type to non-doped depletion type, which fundamentally alters the transistor's electrical characteristics. This parameter change allows the NMOS transistor to operate effectively across the entire voltage range including near ground potential, eliminating the need for PMOS transistor switching and thereby reducing amplitude difference deviation while maintaining Rail-to-Rail operation capability
2Device complexity
If only NMOS transistor pair is used, then the circuit complexity is reduced, but the Rail-to-Rail operation cannot be achieved in conventional configurations
Solution Approach 1:
By changing the NMOS transistor to a non-doped depletion type, the patent enables a single NMOS transistor pair to achieve Rail-to-Rail operation. The non-doped depletion type NMOS transistor has unique characteristics that allow it to function properly across the entire voltage range from ground to power supply voltage, eliminating the need for PMOS transistor pair and simplifying the circuit while maintaining full voltage range adaptability
3Measurement precision
If enhancement type NMOS transistors are used, then the transistor operates well in intermediate voltage range, but the operation near ground voltage causes switching and amplitude difference deviation
Solution Approach 1:
The patent changes the NMOS transistor from enhancement type to non-doped depletion type, which fundamentally alters the threshold voltage and conduction characteristics. This parameter change enables the transistor to maintain stable operation near ground voltage without switching behavior, while preserving excellent performance in the intermediate voltage range, thereby improving both reliability and precision across the entire voltage spectrum
Data Source
AI summary
A differential amplifier circuit includes: an NMOS transistor pair connected with a non-inversion input terminal and an inversion input terminal; a PMOS transistor pair connected with the non-inversion input terminal and the inversion input terminal; and an output circuit section. The PMOS transistor pair includes first and second PMOS transistors, and the NMOS transistor pair includes first and second non-doped type NMOS transistors as a depletion type of NMOS transistors in which a channel region is formed in a P-type substrate without a P well. The output circuit section includes a first current mirror of a folded cascode type connected with the first and second non-doped type NMOS transistors, and outputs an output voltage in response to a current from the first current mirror.