Amplifier Bias Control Circuit With Safe Power-Up Sequencing
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Solution Overview
Problem
Existing amplifier bias control systems rely on sense resistors in series with the amplifier, which can be inaccurate and prone to damage due to excessive current during power-up/power-down sequences, especially in high-current driver amplifiers.
Innovation Solution
An active bias control circuit that senses input current using a scaled-down replica, eliminating the need for a sense resistor in series with the amplifier, and includes a low dropout regulator, current sense circuit, and amplifier control circuit to regulate the input current and manage power sequencing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is used in series with the amplifier to sense input current, then current sensing is achieved, but the system becomes inaccurate and prone to damage due to excessive current during power-up/power-down sequences
Solution Approach 1:
The patent introduces an intermediary current sense amplifier that senses the input current without requiring a large series sense resistor. This intermediary device provides accurate current sensing while isolating the amplifier from excessive current during power-up/power-down sequences, resolving the contradiction between measurement precision and reliability
Solution Approach 2:
The patent implements preliminary power-up/power-down sequencing control that prevents excessive current from reaching the amplifier before bias control is established. By controlling the power sequence in advance, the system avoids damage while maintaining accurate current sensing through the sense amplifier
2Strength
If a large sense resistor is used to handle high quiescent current (>1 A), then the resistor can handle the current, but the resistor must be both large enough to handle current and accurate enough not to cause part to part variation
Solution Approach 1:
The patent segments the current sensing function from the power handling function. The sense amplifier handles the sensing of high current (>1 A) with high precision, while separate power management circuitry handles the current handling capability. This segmentation allows each component to be optimized for its specific function without the trade-off present in using a single large sense resistor
Solution Approach 2:
The current sense amplifier acts as an intermediary that enables precise measurement of high quiescent current without requiring a large, imprecise sense resistor. The sense amplifier provides the measurement precision needed for high current applications while the power management circuitry ensures the current handling capability
3Productivity
If drain voltage is applied before the bias generator is properly turned on, then power delivery is achieved, but excessive current will pass through the amplifier, possibly damaging it
Solution Approach 1:
The patent implements preliminary power-up sequencing that ensures the bias generator is properly turned on before drain voltage is applied to the amplifier. This preliminary action prevents excessive current from passing through the amplifier during startup, resolving the contradiction between fast power delivery and amplifier protection
Solution Approach 2:
The patent uses feedback control through the current sense amplifier to monitor the amplifier's current status and control the power delivery sequence. This feedback mechanism ensures that drain voltage is only applied when the bias generator is ready, preventing excessive current while maintaining efficient power delivery
Data Source
AI summary
An active bias control circuit for an amplifier includes a low dropout regulator for providing a regulated voltage to provide an input current to the amplifier, and a current sense circuit responsive to the low dropout regulator for sensing a scaled down replica of the input current to the amplifier. An amplifier control circuit adjusts a control voltage to the amplifier in response to the sensed, scaled down replica of the input current to regulate the input current to the amplifier. A method for power up sequencing an amplifier for an active bias control circuit for the amplifier is also disclosed.