A Digitally Programmable Polyphase Filter for Bluetooth

King Fahd University of Petroleum & Minerals KFUPM, Department of Electrical Engineering A Digitally Programmable Polyphase Filter for Bluetooth By Hussain Alzaher & Noman Tasadduq

OUTLINE • INTRODUCTION • Motivation • Research goals • BLUETOOTH RECEIVER • PROPOSED APPROACH • CMOS IMPLEMENTATION • Current Follower (CF) • Introducing the tuning element (DCCF) • Voltage Follower (VF) • PROPOSED FILTERS • Filter 1 • Filter 2 • EXPERIMENTAL RESULTS • CONCLUSION

INTRODUCTION • Motivation • Use of active polyphase filters is renewed as they provide the solution for image rejection in low-IF wireless applications. • Active-RC filters. • High dynamic range. • Capacitor and/or resistor arrays (matrices) for tuning require relatively large silicon area. • Switching transistors, associated with finite non-linear resistances, degrade the linearity. • gm-C filters • Digitally programmable. • Poor linearity. • Limited dynamic range.

INTRODUCTION • Research Goals • Design Voltage-Mode Polyphase Filter. • Simple active elements; Current follower (CF) and Voltage follower (VF). • Introduce the Programmability Feature. • Use highly linear current division network (CDN) • Investigate the Characteristics of the Proposed Filter. • Implement and Experimentally Test the Fully Differential Version for Low-IF Bluetooth receiver. • Compare Proposed Design with Existing Solutions.

LOW-IF BLUETOOTH RECEIVER • Low-IF Receiver Architecture • 1MHz < IF < 10MHz • Image problem

PROPOSED APPROACH • Systematic Approach • Lowpass filter can be converted to a bandpass polyphase filter centered at ωc. • General Transfer Function of a polyphase filter:

CMOS IMPLEMENTATION • Current Follower (CF) Ix= Iz Vx= 0

CMOS IMPLEMENTATION • Introducing the Tuning Element • Current Division Network (CDN) • Inherently linear. • Input current is binary weighted. • Output current can be expressed as:

CMOS IMPLEMENTATION • Introducing the Tuning Element • Digitally Controlled CF (DCCF) with

CMOS IMPLEMENTATION • Voltage Follower

PROPOSED FILTERS • Filter 1 • Independent control of ωc only using capacitor arrays.

PROPOSED FILTERS • Filter 2 • Independent control of • ωc by adjusting the gain (a). • Q by adjusting R. • Filter gain by adjusting Ri. • Internal nodes either at virtual ground or low impedance.

EXPERIMENTAL RESULTS • Fully balanced 6th-order polyphase filter for a low-IF Bluetooth receiver is designed for Filter 2. • TSMC CMOS 0.35mm (MOSIS) • Supply Voltage ±1.35V. • Total Supply Current 1mA. • 6-bit CDN used for tuning. • Center frequency 3MHz. • Bandwidth 1MHz. • Total Area 0.65mm2.

EXPERIMENTAL RESULTS • Magnitude response showing center frequency tuning

EXPERIMENTAL RESULTS

COMPARISON WITH LITERATURE • B. Shi, W. Shan, and P. Andreani, 2002, “A 57dB image band rejection CMOS gm-C polyphase filter with automatic frequency tuning for Bluetooth,” Proc. Int. Symp. Circuits and Systems, ISCAS’ 2002., vol. 5, pp. V-169 - II-172, 2002. • A. Emira, and E. Sánchez-Sinencio, “A pseudo differential complex filter for bluetooth with frequency tuning,” IEEE Trans. Circuits and Syst.-II, vol. 50, pp. 742 – 754, October 2003. • B. Guthrie, J. Hughes, T. Sayers, and A. Spencer, “A CMOS gyrator Low-IF filter for a dual-mode Bluetooth/ZigBee transceiver,” IEEE J. Solid-State Circuits, vol. 55, no. 9, pp. 1872-1878, Sep. 2005. • C. Psychalinos, “Low-voltage log-domain complex filters,” IEEE Trans. Circuits and Syst.-II, vol. 55, no. 11, pp. 3404- 3412, Dec. 2008.

COMPARISON WITH LITERATURE

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CONCLUSION • xxxxxx

A Digitally Programmable Polyphase Filter for Bluetooth