MOSFET Output Stage Circuit With Process-Tracking Drive Current
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Solution Overview
Problem
Existing output stage circuits produce a constant driving current, which can damage feedback circuits and loads due to the inability of the gate voltage of P-type metal-oxide-semiconductor transistors to vary with process changes, leading to non-variable driving currents.
Innovation Solution
The output stage circuit incorporates a diode-connected P-type or N-type metal-oxide-semiconductor transistor to vary the gate voltage of another transistor, allowing the driving current to adjust with process changes by using a current source and specific transistor configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate voltage of the P-type metal-oxide-semiconductor transistor is pulled down to ground, then the transistor is turned on and the output voltage is pulled up, but the driving current becomes constant and cannot vary with process changes
Solution Approach 1:
The patent changes the gate voltage parameter from a fixed ground reference to a variable reference that tracks process changes. By coupling the gate terminal to the drain terminal through a diode-connected transistor configuration, the gate voltage becomes VGG = VDD - VDS, where VDS varies with process parameters. This allows the driving current ID = kp*(VSG - Vt)^2 to automatically adjust with process variations, resolving the contradiction between maintaining reliable transistor operation and adapting to process changes.
2Device complexity
If the driving current is kept constant, then the circuit operation is simplified, but the feedback circuit and load may be damaged due to inability to accommodate process variations
Solution Approach 1:
The patent implements a feedback mechanism where the drain voltage of the diode-connected transistor feeds back to its gate terminal. This creates a self-regulating system where the gate voltage automatically adjusts based on the transistor's drain-source voltage, which varies with process parameters. The feedback loop ensures that the driving current adapts to process changes without requiring complex external control circuits, thus maintaining simplicity while preventing damage to coupled circuits.
Data Source
AI summary
An output stage circuit includes a first P-type metal-oxide-semiconductor transistor, a second P-type metal-oxide-semiconductor transistor, an N-type metal-oxide-semiconductor transistor, and a current source. A voltage of a third terminal of the first P-type metal-oxide-semiconductor transistor is a first voltage minus a voltage drop between a first terminal and a second terminal of the first P-type metal-oxide-semiconductor transistor. The N-type metal-oxide-semiconductor transistor is coupled between the third terminal of the first P-type metal-oxide-semiconductor transistor and the current source. A second terminal of the second P-type metal-oxide-semiconductor transistor is coupled to the third terminal of the first P-type metal-oxide-semiconductor transistor. When a second terminal of the N-type metal-oxide-semiconductor transistor receives a kick signal, a driving current flowing through the second P-type metal-oxide-semiconductor transistor is relevant to the voltage of the third terminal of the first P-type metal-oxide-semiconductor transistor.