Push-Pull PA Biasing With Series Capacitors for Low Loadline
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Solution Overview
Problem
Existing push-pull power amplifiers face challenges in achieving a low loadline and high common-mode rejection ratio (CMRR) due to parasitic inductances and leakage inductances introduced by wirebond connections and transformer windings.
Innovation Solution
The implementation of tunable capacitors coupled in series between the power amplifier and the balun, allowing for independent tuning of capacitance to balance parasitic and leakage inductances, thereby reducing the loadline and enhancing CMRR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wirebond connections and transformer windings are used in push-pull power amplifiers, then electrical connectivity is achieved, but parasitic inductances and leakage inductances are introduced that increase the loadline and degrade common-mode rejection ratio
Solution Approach 1:
Series capacitors are introduced as intermediary components between the power amplifier outputs and the balun transformer. These capacitors form resonant circuits with the parasitic inductances of wirebond connections and the leakage inductance of the transformer, creating a compensating effect that cancels out the harmful inductive reactance and reduces the loadline.
Solution Approach 2:
The capacitance values of the series capacitors are specifically selected and tuned to match the parasitic inductance parameters of the wirebond connections and transformer. By adjusting the capacitance parameter, the resonant frequency is set to operate at the desired frequency range, transforming the harmful inductive effect into a beneficial resonant cancellation effect.
2Ease of operation
If conventional wirebond connections are used to connect power amplifier outputs to balun, then electrical connection is established, but loadline increases due to parasitic inductance
Solution Approach 1:
Series capacitors are inserted as intermediary elements in the electrical connection path between power amplifier outputs and balun. These capacitors do not disrupt the electrical connectivity function but introduce a compensating reactance that cancels the parasitic inductance, thereby reducing the overall loadline without complicating the connection structure.
3Productivity
If transformer windings are used in balun for balanced-to-unbalanced conversion, then signal transformation is achieved, but leakage inductance increases loadline
Solution Approach 1:
Series capacitors are positioned as intermediaries between the power amplifier and transformer, creating a compensating circuit that addresses the leakage inductance of transformer windings. The capacitive reactance cancels the inductive reactance, allowing the transformer to perform signal transformation while the harmful leakage inductance effect is neutralized.
Solution Approach 2:
The capacitance parameter of the series capacitors is specifically selected to match and compensate for the leakage inductance parameter of the transformer windings. This parameter tuning creates a resonant condition that cancels the harmful inductive effect while preserving the transformer's signal transformation capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces the loadline by approximately 15% and significantly improves the common-mode rejection ratio, achieving balanced loadlines across various frequencies.
Implementation Method 1
At least one capacitor is coupled in series between the power amplifier and the balun... balancing the balun includes increasing a common-mode rejection ratio of the wireless device... balance at least one of a parasitic inductance of the at least one first wirebond connection
Implementation Method 2
the first variable capacitance and the second variable capacitance are selected to balance the balun... balance at least one of a leakage inductance of the primary winding
Data Source
AI summary
Examples of the disclosure include a wireless device comprising a power amplifier configured to output a balanced amplified signal, an antenna configured to transmit and receive signals, a balun coupled to the power amplifier and the antenna, and being configured to receive the balanced amplified signal and output, based on the balanced amplified signal, an unbalanced amplified signal to the antenna, and at least one capacitor coupled in series between the power amplifier and the balun.