Programmable TX-CTF Current Switching for Battery-Efficient Linearity
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Solution Overview
Problem
Designing a transmit continuous-time filter (TX-CTF) for multi-mode cellular handsets that meets performance criteria such as high current drive capability, high linearity, low input referred noise, and low bandpass ripple while minimizing current consumption to extend battery life and reduce battery size is challenging, as increasing current consumption leads to high battery drain.
Innovation Solution
A programmable-current TX-CTF system that includes amplifier circuitry and passive circuitry defining filter parameters, with programmable bias current circuitry and control logic adjusting bias current based on transmitter control signals like modulation mode, band, and power signals to optimize performance according to operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TX-CTF current is increased to meet performance requirements (high current drive capability, high linearity, low input referred noise), then performance is improved, but battery current drain increases
Solution Approach 1:
The patent implements dynamic current adjustment by switching between different current sources (first current source for high performance, second current source for low power) based on operating mode. The bias current to the amplifier is programmably adjusted according to modulation mode, band, and power requirements, allowing the system to adapt current consumption to actual performance needs rather than maintaining high current continuously
Solution Approach 2:
The patent changes the electrical parameters (bias current level) of the amplifier circuit based on operating conditions. By programmably adjusting the bias current according to modulation mode (WCDMA, GSM, EDGE), frequency band, and power requirements, the system optimizes the balance between performance metrics (linearity, noise) and power consumption for each specific operating scenario
2Reliability
If TX-CTF current is increased to achieve high current drive capability and low bandpass ripple, then filter performance is improved, but power consumption increases
Solution Approach 1:
The system dynamically adjusts amplifier bias current based on actual operating requirements. When high current drive capability and low bandpass ripple are needed (certain modulation modes or power levels), the first higher current source is enabled. When these requirements are relaxed, the second lower current source is used, thereby reducing power consumption while maintaining adequate filter performance
3Reliability
If TX-CTF current is increased to reduce input referred noise, then signal quality is improved, but battery life decreases
Solution Approach 1:
The system periodically or conditionally switches between high current mode (for low noise performance) and low current mode (for battery conservation) based on modulation mode and power requirements. This allows the high current state to be applied only when signal quality is critical, rather than continuously, thereby extending battery life while maintaining signal quality when needed
Data Source
AI summary
A programmable-current transmit continuous-time filter (TX-CTF) system can be included in a radio frequency (RF) transmitter. The input of the TX-CTF can receive a baseband transmission signal, and the output of the TX-CTF can be provided to an upconversion mixer for conversion to RF for transmission. The TX-CTF includes amplifier circuitry and passive circuitry that together define the filter parameters. The TX-CTF further includes programmable current circuitry that provides a programmable bias current to the amplifier circuitry. The TX-CTF system also includes control logic that receives one or more transmitter control signals and, in response, generates signals that control the bias current provided to the TX-CTF.