Switched-capacitor circuitry for front-end radio frequency signal processing

This technology is a radio frequency (RF) receiver that exclusively uses switches and capacitors to achieve high order front-end filtering of out-of-band (OB) blocking signals for software defined and cognitive radio applications.

Unmet Need: High order filtering and efficient removal of interfering signals

Traditional RF front end systems can use off-chip passive band-select filters, active low noise amplifiers, and active high-order low pass filters for OB blocking. However, software-defined radio or cognitive radio RF receivers must be able to receive signals over a wide band, while also suppressing OB blockers to successfully process RF signals on an integrated chip. For these applications, passive switched-capacitor (SC) N-path filters have been developed for linear front-end filtering. However, current designs have limited stop-band rejection with only 1st order filtering and cannot sufficiently suppress large OB blocker signals.

The Technology: Enhanced RF filtering for software defined radio

This technology is an electronic circuit for receiving RF signals. The receiver uses passive SC circuitry to achieve enhanced stop band rejection with up to 4th order filtering of input RF signals prior to amplification and further processing. The receiver sequentially implements four functions: impedance matching, blocker rejection, down-conversion, and high order filtering using clock-driven SC nodes. The high order front-end filtering allows for overall enhanced linearity during RF signal processing.

This technology achieves 24dBm OB-IIP3 and 14.7dBm B1dB for a 30MHz offset, 6.8 to 9.7dB NF, and >66dB calibrated harmonic rejection ratio.

Applications:

• Cognitive radio systems used in noisy environments
• SDR systems with Quality of Service (QoS) support
• Low-power and/or mobile SDR transceivers
• Low-cost SDR transceivers
• Educational and/or research tool for RF signal processing

Advantages:

• Increases stop band rejection of OB blocking signals
• Resistant to larger OB blocking signals
• Higher order linear SC filtering (4th order vs. 1st order)
• Improved linearity in processing RF signals
• Exclusively uses passive SC components that are easier to scale than active circuits
• Uses CMOS switches to improve stop band rejection
• Removes need for off-chip duplexers
• Simplified circuit design with less variation at scale

Lab Director:

Peter Kinget, Ph.D.

Patent Information:

Patent Status

Related Publications:

• Xu Y., Kinget P.R. “A Chopping Switched-Capacitor RF Receiver With Integrated Blocker Detection” IEEE Journal of Solid-State Circuits, 2018 June; 53(6): 1607-1617.

• Xu Y., Zhu K., Kinget P.R. “A Blocker-Tolerant RF Front End With Harmonic-Rejecting N-Path Filter” IEEE Journal of Solid-State Circuits, 2018 Feb; 53(2): 327-339.

• Xu Y., Kinget P.R. “A Switched-Capacitor RF Front End With Embedded Programmable High-Order Filtering” IEEE Journal of Solid-State Circuits, 2016 May; 51(5): 1154-1167.

• Xu Y., Kinget P.R. “A switched-capacitor RF front end with embedded programmable high order filtering and a +15dBm OB-B1dB” 2015 IEEE Radio Frequency Integrated Circuits Symposium (RFIC). 2015 May: 291-294.

Tech Ventures Reference:

• IR CU15232

• Licensing Contact: Gregory Maskel