Cascode Bias Tracking in Power Amplifiers for Wide-Supply ACLR
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Solution Overview
Problem
Existing power amplifiers face challenges in maintaining optimal performance across a wide range of supply voltages, leading to potential saturation issues and reduced output range, which affects the Adjacent Channel Leakage Ratio (ACLR) and power efficiency.
Innovation Solution
A cascode amplifier circuit with a cascode driving circuit that generates a driving voltage tracking the level of the supply voltage, utilizing a two-stage configuration with a first stage providing a DC voltage and a second stage adjusting the cascode driving voltage based on the supply voltage level, incorporating adjustable current sources for modes like APT and ET.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed bias voltage is used in the cascode amplifier circuit, then the circuit structure is simple, but the output range is reduced and saturation issues occur across wide supply voltage ranges
Solution Approach 1:
The patent implements a dynamic bias voltage generation system where the cascode driving circuit continuously adjusts the bias voltage based on the instantaneous supply voltage level. This dynamic adaptation allows the amplifier to maintain optimal operating conditions across wide supply voltage ranges (e.g., 1.8V to 5.5V), preventing saturation and maximizing output range without requiring complex external calibration circuits.
Solution Approach 2:
The cascode driving circuit incorporates feedback mechanisms that monitor the supply voltage and automatically adjust the cascode driving voltage accordingly. This feedback loop ensures the amplifier operates within its linear region regardless of supply voltage variations, resolving the contradiction between simple fixed-bias structure and adaptable output range.
2Device complexity
If the cascode driving voltage does not track the supply voltage level, then the circuit operation is simple, but saturation occurs and ACLR performance deteriorates
Solution Approach 1:
The patent introduces a cascode driving circuit as an intermediary component between the supply voltage source and the cascode amplifier. This intermediary actively generates a scaled version of the supply voltage (e.g., Vcascode = 0.7 * Vsupply) and applies it to the cascode transistor gate, ensuring proper biasing and preventing saturation while maintaining good ACLR performance across all supply voltage conditions.
3Reliability
If high power is consumed to maintain performance across wide supply ranges, then the amplifier performance is consistent, but power efficiency is reduced
Solution Approach 1:
The patent dynamically changes the bias voltage parameter based on the supply voltage level, rather than using a fixed high power bias setting. The cascode driving circuit scales the bias voltage proportionally with the supply voltage, allowing the amplifier to maintain consistent performance characteristics across wide supply ranges while consuming only the necessary power for each operating condition, thereby improving overall power efficiency.
Data Source
AI summary
A power amplifier system is presented that includes a cascode amplifier circuit configured to amplify a radio frequency signal when powered by a supply voltage and biased by a cascode driving voltage, a supply source configured to provide the supply voltage, and a cascode driving circuit configured to generate the cascode driving voltage based on the supply voltage, the cascode driving circuit including a first stage configured to provide a DC voltage, and a second stage configured to generate the cascode driving voltage that is tracking a level of the supply voltage based on the DC voltage.