Output Buffer Voltage Mitigation Transistor Biasing
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Solution Overview
Problem
Existing output buffers experience waveform distortion and significant reduction in output current when operating at the lower limit of the acceptable power-supply voltage range (3.0 volts), leading to increased overshoot and undershoot in output signals.
Innovation Solution
An output buffer configuration that includes a first MOS transistor with its source terminal applied to the power-supply voltage and a second MOS transistor with its gate terminal supplied with a power-supply bias voltage, generated by a bias generation circuit, to maintain a constant voltage between the gate and source terminals of the second MOS transistor, ensuring consistent output current regardless of the power-supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a fixed bias voltage is applied to the gate terminal of voltage mitigation transistors, then overshoot and undershoot are reduced, but output current becomes considerably lower when power-supply voltage is at the lower limit (3.0 volts)
Solution Approach 1:
The patent applies a dynamic bias voltage to the gate terminal of the voltage mitigation transistor instead of a fixed bias voltage. The bias voltage is adjusted according to the power-supply voltage level, allowing the transistor to maintain appropriate conduction characteristics across different operating conditions. This dynamic adjustment ensures that the transistor provides adequate voltage mitigation while maintaining sufficient output current even when the power-supply voltage is at its lower limit.
Solution Approach 2:
The patent changes the bias voltage parameter based on the power-supply voltage. When the power-supply voltage is low (3.0 volts), a lower bias voltage is applied to maintain the voltage between gate and source terminals within an appropriate range, preventing excessive current reduction. When the power-supply voltage is higher (3.6 volts), a higher bias voltage is applied to maintain proper voltage mitigation. This parameter adjustment resolves the contradiction between overshoot reduction and output current maintenance.
2Object-generated harmful factors
If a fixed bias voltage is applied to the gate terminal of voltage mitigation transistors, then voltage mitigation is achieved, but waveform distortion occurs in output signal when heavy load is connected at lower power-supply voltage
Solution Approach 1:
The patent employs a dynamic biasing scheme where the bias voltage applied to the voltage mitigation transistor is adjusted according to the power-supply voltage level. This dynamic adjustment ensures that the transistor operates in the appropriate conduction region under different loading conditions and voltage levels, preventing waveform distortion while maintaining signal quality even when heavy loads are connected at the lower power-supply voltage limit.
Solution Approach 2:
The patent modifies the bias voltage parameter based on operating conditions. At lower power-supply voltage (3.0 volts), the bias voltage is reduced to maintain the gate-source voltage within an optimal range, preventing the transistor from entering saturation or cutoff regions that would cause waveform distortion. This parameter adaptation ensures reliable output signal quality across the full operating range.
Data Source
AI summary
An output buffer has a first transistor and a voltage mitigation second transistor. The first transistor is configured to generate a voltage value corresponding to the power-supply voltage in response to an input signal. The second transistor is provided between an output line and the first transistor. A gate terminal of the second transistor is applied with a power-supply bias voltage which turns the second transistor on and makes a voltage between gate and source terminals of the second transistor constant in accordance with a power-supply voltage.