A Novel Active Polyphase Filter Employing Frequency-Dependent Image Rejection Enhancement Technique.

Area of Science:

• Electrical Engineering
• Signal Processing

Background:

• Image interference rejection is critical in low intermediate frequency (low-IF) receivers.
• Conventional active polyphase filters (APPFs) suffer from degraded image rejection ratio (IRR) at high frequencies due to secondary pole imbalances.

Purpose of the Study:

• To introduce a frequency-dependent image rejection enhancement technique for APPFs.
• To overcome the limitations of conventional methods by compensating for secondary pole effects.

Main Methods:

• A frequency-dependent image rejection enhancement technique based on secondary pole compensation is proposed.
• The dominant pole frequency of the high-pass filter (HPF) is adjusted to mitigate image interference.
• The proposed active polyphase filter (APPF) was simulated and fabricated using a 180-nm CMOS process.

Main Results:

• Simulations show an IRR improvement of over 30 dB at hundreds of MHz.
• Measured IRR exceeds -31 dB between 95 and 105 MHz.
• The technique demonstrates excellent IRR for quadrature input signals with phase imbalance.

Conclusions:

• The proposed secondary pole compensation technique effectively enhances IRR in APPFs.
• This method overcomes the operating frequency limitations imposed by secondary poles.
• The design offers a robust solution for image interference rejection in high-frequency low-IF receivers.