Parallel Bias Power Amplifier for Low-Power GMSK Linearity
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Solution Overview
Problem
Existing power amplifying circuits in GMSK transmission mode of GSM exhibit high dependency of radio-frequency output signal on radio-frequency input signal and increased slope, particularly at low-power output.
Innovation Solution
A power amplifying circuit comprising multiple power amplifiers connected in stages, with bias circuits and a control circuit that output bias currents and control currents based on a control voltage, featuring a first stage with two power amplifiers connected in parallel and control current outputs that adjust based on threshold voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If bias current is supplied proportional to control voltage or square of control voltage, then power amplifying circuit operates in GMSK transmission mode, but dependency of radio-frequency output signal on radio-frequency input signal and slope increase at low-power output
Solution Approach 1:
The first stage power amplifier is segmented into two parallel amplifiers with different bias current characteristics. One amplifier receives bias current proportional to control voltage, while the other receives bias current proportional to square of control voltage. This segmentation allows the combined output to achieve flattened dependency characteristics at low-power levels while maintaining GMSK transmission mode operation.
2Device complexity
If single power amplifier is used in first stage, then circuit structure is simple, but dependency of output signal on input signal and slope increase at low-power output
Solution Approach 1:
Two parallel power amplifiers in the first stage are merged to work together, with one amplifier handling linear bias current proportionality and the other handling squared bias current proportionality. Their combined output achieves reduced dependency on input signal and reduced slope at low-power levels, while the second stage amplifier processes the combined signal to produce the final output.
Data Source
AI summary
A power amplifying circuit includes multi-stage power amplifiers, bias circuits, and a control circuit. The bias circuits output corresponding bias currents based on corresponding control currents. The control circuit outputs the control currents to the bias circuits based on a control voltage. The power amplifiers include a first stage of first and second power amplifiers connected in parallel electrically. The bias circuits include first and second bias circuits. The control circuit includes first and second current output units. The first current output unit outputs, to the first bias circuit, a first control current which has a first current value when the control voltage is a first threshold voltage, and which increases linearly with the control voltage, and the second current output unit outputs, to the second bias circuit, a second control current, having a second constant current value, when the control voltage is the first threshold voltage or greater.