Low-Impedance LDO Driver Circuit With GM-Boosted Push-Pull Paths
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Solution Overview
Problem
Existing driver circuit designs for low-dropout (LDO) voltage regulators face challenges in achieving low headroom and high bandwidth, which affects the performance of power management circuitry in applications such as voltage-controlled oscillators, analog-to-digital converters, and RF amplifiers.
Innovation Solution
The implementation of a class AB driver circuit with a common path input stage that provides gm-boosting to output stages, allowing for efficient turn-on and turn-off of load transistors, and incorporating a compensation filter to reduce peaking in the closed loop response, thereby achieving low headroom and high bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional driver circuit designs are used, then the circuit can operate with standard headroom and bandwidth, but the power management circuitry size and efficiency are suboptimal
Solution Approach 1:
The driver circuit dynamically switches between class A and class B operation modes based on the operating conditions. The common-path input stage provides gm-boosting that is activated selectively, allowing the circuit to adapt its transconductance and power consumption characteristics to match the required bandwidth and load conditions, thereby achieving high bandwidth with optimized power management circuitry size
Solution Approach 2:
The circuit changes its operational parameters by implementing gm-boosting in the common-path input stage, which modifies the transconductance parameter of the driver circuit. This parameter change enables the circuit to achieve higher bandwidth performance while maintaining efficient power management, as the boosted gm allows for faster response without proportionally increasing the size of power management circuitry
2Speed
If the load transistor is turned on quickly for high bandwidth, then the transient response improves, but the output impedance increases
Solution Approach 1:
The driver circuit is segmented into separate push and pull paths with independent control. The common-path input stage provides differentiated gm-boosting to each path, allowing the circuit to quickly turn on the load transistor through enhanced drive strength while maintaining low output impedance through the complementary action of the segmented push-pull configuration
Solution Approach 2:
The circuit employs feedback mechanisms where the output of the common-path input stage is fed back to modulate the drive signals to the push and pull paths. This feedback ensures that the load transistor turns on quickly in response to transient demands while the feedback control maintains the output impedance at acceptable levels by adjusting the drive signals appropriately
Data Source
AI summary
In an example, a circuit includes an input stage having a control voltage input, a feedback input, a first control output and a second control output. The feedback input is coupled to a driver output. A first path stage has a first voltage input and a third output. The first voltage input is coupled to the first control output, and the third output is coupled to the driver output. A second path stage has a second voltage input and a fourth output. The second voltage input is coupled to the second control output, and the fourth output is coupled to the driver output. A load transistor has a control input coupled to the driver output. The input stage is configured to provide gm-boosting to the first path stage to turn on the load transistor responsive to an output voltage at a voltage output.