Cascode Current-Steering PA for Doherty-Like RF Efficiency
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Solution Overview
Problem
Power amplifiers in RF applications face challenges in balancing efficiency and linearity, particularly when operating with advanced modulation schemes that require amplifiers to be driven several dB from their maximum saturated output power, leading to inefficiencies and increased complexity with traditional Doherty amplifiers.
Innovation Solution
A power amplifier configuration using a carrier and peaking cascode configuration with distinct supply voltages and biasing schemes, allowing the carrier amplifier to dominate at lower output powers and the peaking amplifier to take over at higher powers, while maintaining gain and minimizing discontinuities in AM-AM response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a Doherty amplifier is used to improve PA efficiency, then efficiency is improved, but device complexity increases due to RF input splitter/phase shifter and output combiner
Solution Approach 1:
The patent extracts and removes the complex RF input splitter/phase shifter and output combiner components from the Doherty amplifier architecture, retaining only the essential carrier and peaking amplifier paths with simplified biasing and supply voltage switching to achieve efficiency improvement without the added complexity
Solution Approach 2:
The patent changes the operating parameters by using distinct supply voltages for carrier and peaking amplifiers and implementing dynamic biasing control, allowing the peaking amplifier to be turned on/off based on output power levels, thereby achieving Doherty-like efficiency without the traditional complex signal splitting and combining network
2Reliability
If the amplifier is operated several dB from maximum saturated output power to maintain linearity, then signal integrity is improved, but efficiency deteriorates
Solution Approach 1:
The patent implements dynamic operation by enabling the peaking amplifier only when needed (at higher output power levels) through bias voltage control and supply voltage switching, allowing the amplifier to adapt its operating point dynamically to maintain both linearity and efficiency across different output power conditions
Solution Approach 2:
The patent uses periodic or conditional activation of the peaking amplifier based on output power thresholds, where the peaking path is engaged only when the carrier amplifier approaches its linear operating limit, thereby maintaining signal integrity while improving efficiency across the full power range
3Power
If the peaking amplifier is activated at high output power, then maximum output power is increased, but discontinuity in AM-AM response may occur
Solution Approach 1:
The patent designs the biasing network and supply voltage switching to provide smooth transition and overlap between carrier and peaking amplifier operation, cushioning against potential discontinuities in the AM-AM response by ensuring continuous current delivery from both paths during the transition region
Data Source
AI summary
According to some implementations, a power amplifier (PA) includes a common emitter configured to receive a radio-frequency (RF) signal. The PA also includes a carrier amplifier coupled to the common emitter to form a carrier cascode configuration, a collector of the carrier amplifier provided with a first supply voltage. The PA further includes a peaking amplifier coupled to the common emitter to form a peaking cascode configuration, a collector of the peaking amplifier provided with a second supply voltage greater than the first supply voltage.