Splitter-Driven Push-Pull Power Amplifier Without Balun DC Loss
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Solution Overview
Problem
Conventional power amplifiers face issues such as high local oscillator current consumption, additional component costs for filtering, and efficiency losses due to IR drops and DC-DC buck ripple problems, particularly in open-drain and transformer-based push-pull amplifiers.
Innovation Solution
A splitter-based push-pull power amplifier design utilizing a pair of P-type and N-type transistors with a splitter that receives a common-mode input pair and provides differential output pairs to the transistors, eliminating the need for additional filters and reducing DC current flow through the balun, thereby minimizing power consumption and ripple issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an open-drain power amplifier is used, then the circuit configuration is simple, but high local oscillator current is required which increases power consumption
Solution Approach 1:
The amplifier is divided into a push transistor and a pull transistor that operate in complementary fashion. The push transistor handles the positive half-cycle while the pull transistor handles the negative half-cycle, allowing each transistor to operate more efficiently and reducing the overall current requirement compared to a single open-drain configuration.
Solution Approach 2:
The invention changes the operating parameters by using complementary transistor pairs with optimized biasing conditions. The gate-source voltages and drain currents are carefully controlled to achieve class-AB operation, which reduces the quiescent current while maintaining high efficiency during signal swings.
2Device complexity
If an open-drain power amplifier is used, then the circuit configuration is simple, but additional band pass filters or notch filters are required which increase off-chip component cost
Solution Approach 1:
The invention extracts and eliminates the need for external filtering components by incorporating filtering functionality directly into the push-pull amplifier circuit. The complementary transistor arrangement naturally suppresses second harmonic distortion and half-LO spurs, making external band pass filters or notch filters unnecessary.
Solution Approach 2:
The filtering function is merged with the amplification function in the push-pull configuration. The circuit simultaneously performs power amplification and harmonic suppression, combining multiple functions into a single integrated structure that eliminates the need for separate filter components.
3Reliability
If an output balun with center tap is used in open-drain PA, then the circuit is complete, but large DC current flowing into the balun causes large IR drop which impacts PA efficiency
Solution Approach 1:
Instead of having DC current flow through the balun as in conventional open-drain designs, the invention inverts the approach by using a push-pull configuration where the balun carries only AC signal current. The complementary transistors drive the balun in a balanced manner, eliminating the need for large DC bias current and thus eliminating the IR drop problem.
Solution Approach 2:
The invention uses a symmetric push-pull configuration where the pull transistor mirrors the push transistor's operation. This symmetry allows the balun to carry equal and opposite currents during each half-cycle, resulting in zero net DC current through the balun and eliminating resistive losses.
4Loss of energy
If a transformer-based push-pull PA is used, then the disadvantages of open-drain PA are overcome, but large DC-DC buck ripple problem occurs
Solution Approach 1:
The invention introduces a novel output stage configuration that acts as an intermediary between the DC-DC converter and the load. This push-pull arrangement with complementary transistors and balun provides galvanic isolation and impedance transformation without requiring a large output transformer, thereby reducing the ripple current while maintaining the benefits of push-pull operation.
Data Source
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AI summary
A push-pull power amplifier (PA) includes a pair of P-type transistors, a pair of N-type transistors, and a splitter, wherein source terminals of the pair of P-type transistors are coupled to a first reference voltage, source terminals of the pair of N-type transistors are coupled to a second reference voltage, and drain terminals of the pair of P-type transistors and drain terminals of the pair of N-type transistors are coupled to an output port of the push-pull PA. The splitter is arranged to receive a common-mode input pair, and provide two differential output pairs to the pair of P-type transistors and the pair of N-type transistors, wherein one of the two differential output pairs is provided to gate terminals of the pair of P-type transistors, and the other of the two differential output pairs is provided to gate terminals of the pair of N-type transistors.