CMOS Transmitter Switch Circuit for High Voltage Swing Isolation
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Solution Overview
Problem
Implementing a switching function in bulk CMOS for transmit modules is challenging due to large voltage swings, which can cause breakdown of MOS transistors and result in distortion and harmonic interference, making it difficult to avoid power loss and ensure reliable operation in GSM and EDGE phones.
Innovation Solution
A switching circuit is designed with a capacitor or inductor network that provides low impedance during transmit mode, limiting the voltage swing experienced by MOS switches, allowing the switch to operate at a node tied to ground, thereby reducing the impact of high voltage swings and preventing breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a switching function is implemented in bulk CMOS for transmit modules, then the device complexity is reduced and integration is improved, but the large voltage swings cause breakdown of MOS transistors and distortion
Solution Approach 1:
The patent introduces an intermediary circuit between the high-voltage transmit path and the bulk CMOS switch. This intermediary transforms the large voltage swing (33 dBm into 50Ω which is 10V RMS swing) into a smaller voltage swing that the bulk CMOS transistor can handle without breakdown. The intermediary acts as a mediator that adapts the voltage levels, allowing the switch to operate reliably in bulk CMOS process.
Solution Approach 2:
The patent changes the voltage parameter by using a transformation circuit that converts the large voltage swing at the antenna port into a smaller voltage swing for the MOS transistor. This parameter transformation allows the switch to operate within the safe operating range of bulk CMOS transistors, avoiding breakdown and distortion issues while maintaining the switching function.
2Ease of operation
If a switch handles large voltage swings in the transmit path, then the switching function is achieved, but power loss is contributed to the TXM
Solution Approach 1:
The patent replaces the traditional mechanical or GaAs-based switch with a bulk CMOS transistor-based switch controlled by an intermediary circuit. This substitution allows for lower power consumption while achieving the same switching function. The bulk CMOS transistor, when properly controlled through the voltage transformation, consumes less power than traditional switch implementations in the transmit path.
3Ease of operation
If the reverse biased diode to substrate is forward biased due to large voltage swings, then the switching function operates, but non-linear capacitor generates unwanted harmonic interference
Solution Approach 1:
The patent applies preliminary anti-action by using the intermediary circuit to prevent the reverse biased diode to substrate from becoming forward biased. The voltage transformation occurs before the signal reaches the MOS transistor, thereby preventing the harmful condition of diode forward biasing that would generate non-linear capacitance and harmonic interference. This preliminary prevention eliminates the harmful effect before it can occur.
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 enables the implementation of a front-end switch in bulk CMOS without power loss, ensuring reliable operation and reducing the risk of transistor breakdown, while maintaining functionality for both transmit and receive modes in GSM and EDGE communication systems.
Implementation Method 1
A switching circuit is designed with a capacitor or inductor network that provides low impedance during transmit mode, limiting the voltage swing experienced by MOS switches
Data Source
AI summary
Transmit modules typically constitute passive matching circuitry, harmonic trap filters and an antenna switch to provide isolation between the transmit bands as well as between transmit and receive functions. In complementary metal-oxide semiconductor (CMOS) processes the switch function is difficult to implement as a large voltage swing may result in breakdown of the MOS oxide, drain diode, source diode as well as substrate diodes. Therefore a switching function is provided at a node that has low impedance during transmit that limits the voltage swing that the MOS switches experience. The approach is particularly useful, but not limited to, half duplex transmissions such as those used in global system for mobile (GSM) communication, enhanced data for GSM Evolution (EDGE), and time division synchronous code division multiple access (TDSCDMA).