Amplifier Active Bias Circuit Without Series Sense Resistor
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing amplifier systems rely on sense resistors in series with the amplifier, which dissipate power and require accurate trimming, and also face challenges in proper power-up sequencing to avoid damaging the amplifier.
Innovation Solution
An active bias control circuit that senses input current through a scaled-down replica, eliminating the need for a sense resistor and using a switch and current sense circuit to adjust control voltage, and includes a method for safe power-up sequencing to prevent excessive current flow.
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 power dissipation increases and manufacturing precision requirements increase
Solution Approach 1:
The patent creates a scaled-down replica of the amplifier circuit that includes a replica of the sense resistor. This replica allows current sensing to be performed on the copied circuit rather than the actual amplifier, eliminating the need for a physical sense resistor in series with the amplifier. The replica current is proportional to the actual amplifier current, providing accurate sensing without the power loss of a series resistor.
Solution Approach 2:
The patent introduces an intermediate scaled-down replica circuit that mediates between the amplifier and the sensing mechanism. Instead of directly sensing current through a series resistor (which causes power loss), the system uses this intermediate replica to provide sensing information. The replica acts as a buffer that transfers sensing functionality without the harmful side effects of power dissipation.
2Measurement precision
If a sense resistor is used in series with the amplifier, then current sensing is achieved, but device complexity and trimming requirements increase
Solution Approach 1:
By copying the sense resistor into a scaled-down replica of the amplifier circuit, the patent eliminates the need for external sense resistors and their associated trimming mechanisms. The replica is created using standard transistor scaling techniques, which are already integrated into the amplifier design process, thereby reducing overall device complexity while maintaining sensing accuracy.
3Ease of operation
If drain voltage is applied before bias generator is properly turned on, then power-up sequence is simplified, but excessive current damages the amplifier
Solution Approach 1:
The patent implements preliminary action by using the scaled-down replica circuit to predict and control the amplifier's current draw before full power is applied. The replica allows the bias generator to be pre-configured and the power-up sequence to be carefully orchestrated, ensuring that the amplifier is properly biased before drain voltage is applied, thus preventing excessive current while maintaining a manageable power-up procedure.
4Power
If quiescent current is increased to handle large current amplifiers (>1A), then sense resistor can be larger, but part-to-part variation increases
Solution Approach 1:
The patent scales down the entire amplifier circuit including the sense resistor, allowing the system to handle large quiescent currents (>1A) in the actual amplifier while the replica operates at lower currents. This scaling approach maintains consistent part-to-part variation characteristics because the replica uses the same fabrication process and component ratios as the amplifier, just at different current levels. The proportional relationship remains accurate regardless of the absolute current magnitude.
Data Source
AI summary
An active bias control circuit for an amplifier includes a switch responsive to a supply voltage for providing an input current to the input of the amplifier, and a current sense circuit coupled to the switch for sensing a scaled down replica of the input current to the amplifier. A first amplifier control circuit is responsive to the current sense circuit for adjusting a first 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. Circuitry for power up sequencing an amplifier for an active bias control circuit for the amplifier is also disclosed.