Push-Pull PiN Diode RF Switch for Low-Dissipation Linearity
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Solution Overview
Problem
PiN diode configurations in RF switch circuits can only sink, not source, large ac current swings, leading to a trade-off between linearity and dc power dissipation, particularly in high-power applications like 5G base stations.
Innovation Solution
A push-pull diode-based configuration is introduced, where a first PiN diode device is configured to sink or source alternating current, and a second diode-based device is used to complement it, allowing both current sourcing and sinking, thereby eliminating the need for Class-A biasing and reducing dc current dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a unidirectional PiN diode is used as a shunt switch, then the circuit can sink current, but it cannot source large ac current swings, requiring Class-A biasing which increases dc power dissipation
Solution Approach 1:
The single PiN diode is segmented into two separate PiN diodes (first and second PiN diodes) that operate in a push-pull configuration. Each diode handles one direction of current flow, allowing the circuit to both source and sink current swings without requiring Class-A biasing of a single diode, thereby reducing dc power dissipation while maintaining linearity.
Solution Approach 2:
Two PiN diodes are merged into a single push-pull switching unit that replaces the traditional single shunt switch. This combined configuration allows bidirectional current handling (sourcing and sinking) and enables Class-AB or Class-C biasing modes, significantly reducing the dc bias current requirement compared to Class-A operation of a single diode.
2Reliability
If the bias current is increased to improve linearity in a single PiN diode configuration, then linearity performance improves, but dc power dissipation increases significantly
Solution Approach 1:
The current handling function is segmented between two PiN diodes, allowing each diode to operate with lower individual bias currents while collectively handling the full signal swing. This segmentation enables the use of more efficient biasing modes (Class-AB or Class-C) that reduce overall dc power dissipation while maintaining the required linearity performance.
3Reliability
If a single PiN diode is biased in Class-A mode to handle large current swings, then linearity is maintained, but efficiency decreases due to high dc bias current
Solution Approach 1:
Two PiN diodes are merged into a push-pull configuration that enables efficient Class-AB or Class-C biasing. This combined structure allows the circuit to maintain high linearity performance while operating at lower dc bias currents, thereby improving overall system efficiency compared to Class-A operation of a single diode.
Solution Approach 2:
The push-pull configuration with two diodes enables periodic action where each diode conducts during alternate half-cycles of the signal. This periodic conduction pattern allows the use of Class-AB or Class-C biasing modes, where diodes are not continuously conducting, thereby reducing dc power dissipation and improving efficiency while maintaining linearity during the active conduction periods.
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 configuration achieves high linearity while significantly reducing dc current dissipation, from 100 mA to 5 mA, by allowing the PiN diode to be biased in a Class-AB mode, thus improving efficiency and performance in RF switch circuits.
Implementation Method 1
A PiN diode typically behaves as a current-controlled non-linear resistor and capacitor/varactor at radio and microwave frequencies. Like the conventional PiN diode, it allows current flow in one direction when forward biased, but not in the other when it is reverse biased.
Implementation Method 2
RF PiN diode switches are often realised on a printed circuit board or a monolithic microwave integrated circuit that utilises quarter wavelength (λ/4) transmission lines (TLs)
Implementation Method 3
since the undoped intrinsic semiconductor region in PiN diodes decrease the off-state capacitance when reverse-biased, the PiN diode is often the preferred RF switch to use due to its much better insertion loss and higher isolation performance
Data Source
AI summary
A radio frequency, RF, switch circuit (201, 301, 401, 501, 601, 701, 751, 801) includes at least one first PiN diode device (252, 352, 452, 552, 652, 752, 852, 945) configured to sink or source a first alternating current; and an impedance inversion circuit (222, 322, 422, 522, 622, 722, 822, 922), connected to the at least one first PiN diode device and arranged to provide a transformed impedance between a first side of the impedance inversion circuit and a second side of the impedance inversion circuit. The RF switch further includes a second diode-based device (254, 354, 454, 554, 654, 754, 854, 945) configured to source or sink a second alternating current; and a bias circuit (330, 430, 530, 630, 830, 930) connected to at least one of the at least one first PiN diode device and the second diode-based device, wherein the at least one first PiN diode device cooperates with the second diode-based device as a push-pull current circuit.