Multi-band Amplifier Harmonic Suppression via Shunting Circuit
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Solution Overview
Problem
Conventional power amplifiers for wireless communication devices face challenges in miniaturization due to high RF transmission power, leading to non-linear distortion and harmonic energy issues, especially when multiple frequency bands are supported, as second harmonics from lower frequency bands interfere with higher frequency bands, causing compliance failures with regulatory standards.
Innovation Solution
An amplifier circuit with a first and second power amplifier for different frequency bands, a control circuit to turn on/off each amplifier, and a shunting circuit to attenuate harmonic signals from the lower frequency band, integrated on a single semiconductor die, ensuring high-linearity RF power amplification without attenuating higher frequency signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If separate output power amplifiers and transmission paths are used for each frequency band, then the desired output power levels are achieved, but harmonic energy from the low frequency band interferes with the high frequency band
Solution Approach 1:
A shunting circuit is introduced as an intermediary component between the low frequency band transmission path and the high frequency band transmission path. This shunting circuit selectively couples second harmonic energy from the low frequency band to ground, preventing it from interfering with the high frequency band while allowing the desired output power levels to be maintained in both bands
2Reliability
If pass filters are employed for each transmission path, then undesired signals are prevented from being conveyed to the diplexer, but second harmonic energy from the low frequency band is passed with very low loss
Solution Approach 1:
The shunting circuit extracts second harmonic energy from the low frequency band transmission path by providing a selective coupling path to ground. This extraction occurs at the source of the harmonic interference, removing the harmful frequency components before they can propagate to the high frequency band, while the pass filters continue to perform their primary function of blocking undesired signals
3Object-generated harmful factors
If an LC trap circuit is used to attenuate second harmonic energy, then harmonic suppression is achieved, but signals in the higher frequency band are also attenuated
Solution Approach 1:
The shunting circuit implements local quality by being selectively coupled to ground only at the specific frequency of the second harmonic of the low frequency band. This frequency-selective coupling allows the circuit to attenuate only the harmful harmonic energy while leaving the desired high frequency band signals unaffected, avoiding the broad attenuation problem of conventional LC trap circuits
Data Source
AI summary
An amplifier circuit includes a first power amplifier that can produce a first amplified signal in response to a first input signal in a first frequency band, and a second power amplifier that can produce a second amplified signal in response to a second input signal in a second frequency band. A center frequency of the second frequency band is higher than the a center frequency of frequency band A control circuit can turn on or turn off the first power amplifier and configured to turn on or turn off the second power amplifier. A shunting circuit is coupled to an output of the second power amplifier. The shunting circuit can attenuate harmonic signals from the first frequency band under the control of the control circuit.