Dynamic Bias RF Switch for Faster Wi-Fi Signal Switching
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Solution Overview
Problem
Existing fast switches for Wi-Fi applications face limitations due to the use of RF coupling capacitors, which increase switch size and power level limitations, and high impedance charge pumps that result in slow switching times.
Innovation Solution
An integrated RF switch with a dynamic bias circuit that includes a change of state detector, pulse generator, and improved driver bias generator, which increases bias current momentarily during switching to reduce propagation delay and maintain low average current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If RF coupling capacitors are used to AC couple the RF signal to the output load, then the bias voltage swing can be driven from -Vdd to 0V, but the switch size increases and power level is limited
Solution Approach 1:
The patent removes the RF coupling capacitor from the circuit by implementing DC coupling between the common node and output load. This extraction of the capacitor eliminates the size penalty while enabling higher power levels through increased bias voltage swing capability.
Solution Approach 2:
The patent changes the coupling method from AC to DC, which fundamentally alters the operating parameters. DC coupling allows the bias voltage to swing from -Vdd to +Vdd instead of being limited to -Vdd to 0V, thereby increasing power level without requiring large capacitors.
2Reliability
If a charge pump is used to generate negative bias voltage, then negative voltage can be provided to control FETs, but the high impedance results in slow switching times
Solution Approach 1:
The patent implements a dynamic bias circuit that adjusts the bias current based on switching state. During switching transitions, the circuit provides high current to rapidly charge/discharge parasitic capacitances, while during steady state it maintains lower current for power efficiency. This dynamic adjustment resolves the contradiction between fast switching and power consumption.
Solution Approach 2:
The bias circuit operates in periodic cycles: high current mode during switching transitions and low current mode during steady state operation. This periodic action allows the system to achieve fast switching when needed while minimizing average power consumption during normal operation.
3Speed
If increased static source and driver impedance is used to allow faster switching, then switching speed improves, but average current and solution size increase
Solution Approach 1:
The patent employs dynamic impedance adjustment where the source and driver impedance are high only during switching transitions to enable fast charging/discharging of capacitances, then return to low impedance during steady state to minimize average current consumption. This temporal separation resolves the contradiction between switching speed and power consumption.
Data Source
AI summary
An integrated radio frequency (RF) switch and method of outputting one RF signal from a plurality of RF signals is provided. The integrated RF switch comprises an input decoder, a plurality of level shifter/drivers, a negative voltage generator and a dynamic bias circuit. The input decoder determines which one of the plurality of RF signals to output. Each one of the plurality of level shifter/drivers controls output of one of the plurality of RF signals. The negative voltage generator creates a negative voltage to drive the plurality of level shifter/drivers. The dynamic bias circuit generates a bias current for the plurality of level shifter/drivers, detects a change of state from the input decoder, generates a pulse in response to detecting the change of state, and increases the bias current for the plurality of level shifter/drivers for a duration of the pulse to decrease a switching time between two RF signals.