A CMOS Low Power Current-Mode

Polyphase Filter

ByHussain Alzaher & Noman Tasadduq

King Fahd University of Petroleum & Minerals

KFUPM, Department of Electrical Engineering

2

OUTLINE INTRODUCTION

Bluetooth receiver Available solutions

PROPOSED APPROACH CURRENT AMPLIFIER

Introduction Fully differential current amplifier (FDCA)

BASIC PRINCIPLE PROPOSED FILTER

Single ended realization Fully differential realization

EXPERIMENTAL RESULTS COMPARISON WITH THE LITERATURE CONCLUSION

3

Low-IF Receiver Architecture Unlike zero-IF: Low-IF = No DC offset and

flicker noise problems Image problem Solution: Polyphase bandpass filter

INTRODUCTION

LNA

LO1

LO2

BPF-45

+45

Amplifier tLimiterFSK-

Demodulator

LPF

o/p+

-

4

INTRODUCTION

Available SolutionsActive-RC filters.

High dynamic range. Limited bandwidth. Relatively high power consumption.

gm-C filters High frequency. Programmable. Poor linearity=Limited dynamic range.

5

PROPOSED APPROACH

Design new polyphase filter based on optimum active element

Higher bandwidth than op-amp lower power

Better linearity than gm better DR

6

PROPOSED APPROACH

Current-mode processing inherently possess High BW + Low voltage Low Power High signal swing High linearity

Current Amplifier based Filter Simple filter topology Low power

7

CURRENT AMPLIFIER (CA)

Introduction Conveys input current from a low impedance input terminal

(X) to a high impedance output terminal (Z).

Gain=K, (sizing of current mirror transistors).

Two types: positive CA (input and output currents are both going in the same direction) and negative CA (having currents in opposite directions).

IX

X ZpCAKIX IX

X ZnCAKIX

CA with +ve output CA with -ve output

8

IX

XZn

ZpCA

KIX

KIX

Single Input/Dual Output CA

zp zn xI I KI 0xV

M13 M9 M10

M11VDD

M12

ISB

M3

M4

M8

M7

M6

M5

VDD

VSS

X ZpM2 M1

M20

IB Zn

M14

M15

M16

M17

M18

M19

K

1 K

1 K

K

M21

1

1

1

1

Core Input Stage

Class-AB Output Stage

Current Mirrors

CURRENT AMPLIFIER (CA)

9

H. Alzaher, N. Tasadduq, “Realizations of CMOS fully differential current followers/amplifiers," IEEE International Symposium on Circuits and Systems (ISCAS 2009), pp. 1381-1384.

Details available in:

I1

XZn

ZpCA

XZn

ZpCA

I2

I1

I2

I2

I1

Io1=K(I1-I2)

Io2=K(I2-I1)

(K)

(K)

Xp

XnZn

Zp

FDCA

Xp

Xn Zn

Zp Io1

Io2

I1

I2

Four terminal device, with two input and two output currents.

(Ideally common mode gain is zero)01 02 1 22 ( )I I K I I

CURRENT AMPLIFIER (CA)Fully Differential Current Amplifier (FDCA)

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BASIC PRINCIPLE

0 0

/( )

1 ( / / )o o

c

aT j

j

General Transfer function

/ / 2

/

c

c c o

o o

Center frequency

Q BW

Gain a

Image Rejection

( ) /c o oT j a

20

/( )

1 (2 / )o o

c

c

aT j

2( )Image Rejection Ratio 1 16

( )c

c

T jIRR Q

T j

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BASIC PRINCIPLE Systematic Design

Lowpass filter can be converted to a bandpass polyphase filter centered at ωc.

Complex poles are achieved by using cross-coupling between I and Q paths.

s o

ao

c

aoj

xi xo

s o

ao

c

ao

xI xoI

xQ xoQ

c

ao

s o

ao

-

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PROPOSED FILTER Single Ended Realization

R

C

Ii Io

0 0

( )1 ( / / )c

AT j

j

2 /c K RC

1/o RC

2 / 2Q K

Independent control of ωc without changing Q using R

and/or C.

RCA+

+

C

RCA -

+C

K1IoI

K2IoI

K2IoQ

K1IoQ

II

IQ

1A K

Simple LP filter to complex filter

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PROPOSED FILTER

Nominal Values 6th order polyphase filter is implemented. The nominal center frequency of 3MHz and overall

bandwidth of 1MHz are achieved by selecting R1=13k, C1=8.5pF and K2=2.1.

K1 is 1 to achieve a gain of unity.

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PROPOSED FILTER Fully Differential Realization

Zp1

Zn1

Zp2

Zn2

Xp

Xn

Iip

Iin

C

CR

R

Zp1

Zn1

Zp2

Zn2Xp

Xn

Iqp

Iqn

C

CR

R

(to next stage)Ioip

Ioin

Ioqp

Ioqn

}

(to next stage)}

FDCA

FDCA

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PROPOSED FILTERFDCA with four outputs

FDCA

Zp1

Zn1

Zp2

Zn2

Xp

Xn

I1

I2

CA

Zp1

Zn1

Zp2

Zn2

Xp

(K1)

(K2)

CA

Zp1

Zn1

Zp2

Zn2

Xn

(K1)

(K2)

I1

I2

Io1a=K1(I2-I1)

Io2a=K1(I1-I2)

Io1b=K2(I1-I2)

Io2b=K2(I2-I1)

Zp1

Zn1

Zp2

Zn2

FDCA (with four outputs)

01 02 1 1 22 ( )a aI I K I I

01 02 2 1 22 ( )b bI I K I I

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FOUR OUTPUT CA REALIZATION

9 10M M BI I I ; 15 25M M S BI I I ; 8 17 19 23 0.5M M M M SBI I I I I 3M S BI I ;

Core biasing circuit of IB=9A and ISB=3A is shared for all FDCATotal biasing current is(2 6 )x4x6 0.88mAB S B B S BI I I I

M13 M9 M10

M11VDD

M12

ISB

M3

M4

M8

M7

M6

M5

VDD

VSS

X Zp1M2 M1

M20

IB Zn1

M17

M16

M19

M18

M23

M22

1

1 0.5

M21

1

1

1

1

M15

M14

Zp2

1.05

Zn2

M25

M24

0.5 1.05

1.050.50.5 1.05

6M S BI I ;

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EXPERIMENTAL RESULTS

Standard 0.18m CMOS process. Supply Voltage ±1.35V.Total Supply Current 0.88mA.Center frequency 3MHz.Bandwidth 1MHz.Center frequency tuning using

capacitor arrays.

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EXPERIMENTAL RESULTS Signal magnitude response showing center frequency tuning

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EXPERIMENTAL RESULTSFeatures Proposed Filter

fc 3MHz Bandwidth 1MHz Supply voltage 2.7V Total current 0.88mA Tuning Range 1.8-4.5 MHz ATTENUATION 1st Blocker @4MHz 2nd Blocker @5MHz 3rd Blocker @6MHz

14dB (BT specifies 0dB) 37dB (BT specifies 30dB) 52dB (BT specifies 40dB)

IIP3 In-band Out-of-band

29.2dBm 45dBm

Total noise -68dBm SFDR (Inband) 64.7dB (BT specifies more than 50dB) Image rejection >54dB

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COMPARISON WITH LITERATURE

1. 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.

2. 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.

3. 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.

4. C. Psychalinos, “Low-voltage log-domain complex filters,” IEEE Trans. Circuits and Syst.-II, vol. 55, no. 11, pp. 3404- 3412, Dec. 2008.

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COMPARISON WITH LITERATURE

Features [1] [2] [3] [4] Proposed

Filter Technology 0.35m 0.35m 0.18m 0.35m 0.18m

Order 6th 7th 5th 6th 6th Application BT BT BT BT BT

fc 2MHz 3MHz 1MHz 2MHz 3MHz Active

Element gm-C gm-C gm-C

gm-C log dom

CF-C

Tuning gm gm gm gm Cap arrays Supply voltage

2.7V 3.3V 3.6V 1.2V 2.7V

Total current

4.7mA 3.8mA 0.53mA 9.1mA 0.88mA

Power/pole 2.1mW 1.8mW 0.38mW 1.8mW 0.4mW Image

rejection >45dB >57dB >48dB >45.7dB >54dB

SFDR (Inband)

45.2dB 53dB NA 36.9dB 64.7dB

Total Area 1.32mm2 0.54mm2 0.23 mm2 Sim. 0.61 mm2

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COMPARISON RESULTS

Power consumption/pole Proposed filter and [3]

Image rejection Propsed filter and [2]

SFDR Proposed filter

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CONCLUSION

CA based filters inherently exhibit higher bandwidth than active-RC and better linearity than gm-C.

This is demonstrated by a new polyphase filter with improved SFDR and IRR while using relatively lower power.

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Thank You,