international journal of electronics and communication engineering & technology...

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN

0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 1, January- February (2013), © IAEME

256

IMPLEMENTATION OF CMOS 3.8 GHZ NARROW BAND PASS (HIGH

Q) SWITCHED CAPACITOR FILTER IN 180 NM TECHNOLOGY

prashant s. patel1, mehul l. patel

2

1E&C Engg Department, L.C.Institute of Technology, Mehsana, Gujarat, India,

2E&C Engg.Department, L.C.Institute of Technology, Mehsana, Gujarat, India,

ABSTRACT

In the recent era of nano technology, a surging demand for high-quality monolithic MOSFET

active filters in the fields of voice/data communications and instrumentations stimulated

tremendous research and development (R&D) efforts of switched-capacitor filters (SCF). The

most applications in high-frequency communication systems require narrow-bandpass filters

(Q ≈ 20), with a rather tight tolerance in the center frequency accuracy along with operational

amplifier (opamp). In this paper a SCF with the bandpass of 3.8 GHz is reported with the

simulation result obtained in Taiwan Semiconductor Manufacturing Company (TSMC)

180nm Technology using Mentor Graphics Eldo Simulation tools.

KEYWORDS: Bandpass Filter (BPF), CMOS Operational Amplifier, High Quality Factor

Q, Switched Capacitor Filter (SCF)

1 INTRODUCTION

In the VLSI system design, implementation of passive elements such as resistors,

inductors, etc on layout platform creates significant problems for the designers. Further it

requires detail knowledge of the layout process with large layout area. To overcome these

problems, Switched Capacitors (SC) techniques is significantly used instead of resistor. A

resistor can be replaced by a combination of capacitor and two switches operated on toggle

switch condition. The need to have monolithic analog filters motivated circuit designers in

the late 1970s to investigate alternatives to conventional active-RC filters. With the current

through the switched capacitor resistor proportional to the voltage across it, the equivalent

“switched capacitor resistance (Req)” is given by [1],

�� 1�� (1)

Where Fs are the sampling frequency of the filter and C is the capacitor of the circuit.

INTERNATIONAL JOURNAL OF ELECTRONICS AND

COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)

ISSN 0976 – 6464(Print)

ISSN 0976 – 6472(Online)

Volume 4, Issue 1, January- February (2013), pp. 256-263 © IAEME: www.iaeme.com/ijecet.asp

Journal Impact Factor (2012): 3.5930 (Calculated by GISI) www.jifactor.com

IJECET

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257

2. REALIZATION OF A SC FILTER

Realizing a SC bandpass filter such as cascading simple biquadratic filters, ladder band pass

filter or N-path techniques or two operational amplifiers can be implemented by various

methods. All of them, mainly, any high-order transfer function can be realized by using

cascading biquadratic filters and first-order section, generally, the resulting circuit is often

difficult to fabricate and very sensitive to finite op amp gain effects, stray resistance,

capacitance and element-value variations. For filters that have to realize higher Q-value,

ladder filter structure is employed. High capacitance spread ratio and requirement of the same

number of op amps as the filter order for the implementation are the main difficulties in

ladder filter. For achieving even higher Q-values, filter designs based on the concept of N-

path filter may be used. Several difficulties arise since the most high frequency applications

require very narrow band filters. This lead to sensitivity problems because of the rapidly

increased sensitivity of high Q filters for both to the ratio of the capacitors in the filter as well

as the gain and the settling behavior of the operational amplifier used in N path filter.

3. A HIGH Q BANDPASS SC FILTER USING TWO OPERATIONAL AMPLIFIER

In a high Q band pass filter using two operational amplifiers, the quality factor Q of

the circuit is controllable through a single resistance. In general form the transfer function of

a band pass filter is given by [2]

��

�� (2)

Where ao, a1, b1 and b2 are constants

The quality factor Q of the band pass filter is governed by the term b1. It has infinite Q if b1

approaches zero value but practically it is not possible although some high value up to Q≈20

is easily possible.

3.1 Two Stage Cmos Operational Amplifier

Operational amplifiers are key elements in analog processing systems. Operational

amplifiers are an important part of many analog mixed signal systems. As the demand for the

compact integrated circuits increases largely, the design of analog circuits such as operational

amplifiers in CMOS technology becomes more critical. Operational amplifiers (op-amps)

with moderate DC gains, high output swings and reasonable open loop gain band width

product (GBW) are usually implemented with two-stage structures. The op-amp which has

been designed is a two stage CMOS operational amplifier. Design has been carried out in

Mentor graphics tool. Simulation results have been verified using Eldo Simulation. The

simulation results in a TSMC 0.18um CMOS process from a 2.3V voltage supply

demonstrate the designed has a gain 59.98dB.



258

Fig: 1 a general structure of two stage operational amplifier [3]

The general structure of two-stage op-amp is shown in Figure 1.The circuit consists of an

input differential trans-conductance stage which forms the input of the op-amp followed by

common-source second stage. The common source second stage increases the DC gain by an

order of magnitude and maximizes the output signal swing for a given voltage supply. This is

important for reducing the power consumption in two stage operational amplifier. Bias circuit

is provided to establish the operating point for each transistor in its quiescent stage.

Compensation is required to achieve stable closed loop performance. High voltage gain, large

common-mode input range and a small number of transistors required for implementation are

the main advantages of this operational amplifier architecture. This op-amp is a widely used

general purpose op-amp which finds applications in switched capacitor filters, analog to

digital converters and sensing circuits.

3.2 Implementation of Cmos Two Stage Operational Amplifier Using Tsmc 180nm

Technology in Mentor Graphics Tool

Fig: 2 Schematic of two stage CMOS operational amplifier [3]



259

3.3 Simulation Results of Two Stage CMOS Operational Amplifier in TSMC 180nm

Technology using Mentor Graphics Tool.

Fig: 3 Simulation result for AC analysis for two stage operational amplifier in 180nm

technology using Mentor Graphics tool.

Fig: 4 Simulation result of transient analysis of two stage operational amplifier in 180nm

technology using Mentor Graphics tool.



260

3.4 Implementation of Actual Circuit for High Q Band Pass Filter using two stage

operational amplifiers [2].

Fig: 5 Schematic of high Q SC bandpass filters using two stage operational amplifier [2].

Simulation result (frequency response) of high Q SC bandpass filter using IC 3140 which is

an operational amplifier gives the bandpass frequency of 11-40 MHz with the Q value of 1.8

[2].

4. Implementation of CMOS 3.8 GHz Bandpass SC Filter Using Different Voltage

Sources in TSMC 180nm Technology using Mentor Graphics Tools.

Fig: 6 Schematic of CMOS 3.8 GHz bandpass SCF using various voltage sources [4]



261

Fig:7 Simulation result of bandpass filter at 3.8 GHz in TSMC 180nm Technology using

Mentor Graphics Tools.

Here due to some mismatch in transistors parameters and CMOS operational amplifier

operating condition, there is some fluctuation in output result shown in figure 7.

Table:1 Comparison of high Q bandpass SC filter using two operational amplifier [2],

CMOS 2.3 GHz Bandpass SCF using different voltage sources [4] and CMOS 3.8

GHz Bandpass SCF using different voltage sources (my work).

Characteristics

High Q Bandpass

SCF Using Two

Stage Operational

Amplifier[2]

CMOS 2.3 GHz

Bandpass SCF Using

Different Voltage

Sources(350nm,

TSMC)[4]

My Work

(180nm,

TSMC)

Supply Voltage (V) 12 2.3 1.8

Power Dissipation (mW) 58.356 10.356 8.835

Bandpass Frequency 11- 40 MHz 2.2- 2.4 GHz 1.8 - 3.8 GHz

Slew rate N.A. 1.8721MEG 1.5955MEG

Possible Q value ≈1.8 ≈26 ≈28



262

5. CONCLUSION

In most high frequency applications which require very narrow band filters which

lead to sensitivity problems because of the rapidly increased sensitivity of high Q filters.

Though the sufficient level of sensitivity is achieved and the bandpass of 3.8 GHz with high

Q≈28 value is achieved. This structure can further be explore using 90nm, 65nm, etc. and the

still high value of Q (≥28) can be achieved. From both the implementation method discussed

in this paper, implementation of CMOS 3.8 GHz bandpass filter using different voltage

sources is more preferable due to its low power dissipation and high Q value. The most

desired application of narrow bandpass filter includes fast data/voice communication and

instrumentation.

REFERENCES

[1] Mingliang Liu, Demystifying switched capacitor circuits (UK: Library of Congress

Catalog, ISBN 13: 978-0-7506-7907-7).

[2] Seema Rana, Kapil Sharma, Kirat Pal, High Q band pass filter using two operational

amplifiers, journal of physical sciences, Vol. 11, 2007, 133-138, April-2007

[3] Phillip E. Allen, Douglas R. Holberg, CMOS analog circuit design, second edition

(New York: Oxford University Press, 2002) 243-415.

[4] David Cordova, Jorge Cruz, Carlos Silva, A 2.3 GHz CMOS high Q bandpass filter

design using an active inductor, XV workshop iberchip, Buenos Aires - Argentina, 25

- 27 de Marzo de, 2009.

[5] Amana Yadav, A review paper on design and synthesis of two stage CMOS Op-Amp,

International journal of advances in engineering & technology, ISSN: 2231-1963, Jan

2012

[6] Jose Silva Martinez, Edgar Sanchez Sinencio, Switched capacitor filter, (Texas a&M

University, CRC Press LLC, Jan-2003) 85.1-85.6.

[7] Rajinder Tiwari, R. K. Singh, Ganga Ram Mishra, “A New Approach For Design Of

Cmos Based Cascode Current Mirror For Asp Applications”International journal of

Electronics and Communication Engineering &Technology (IJECET), Volume 2,

Issue 2, 2011, pp. 01-07, Published by IAEME.

[8] Ms.Rashmi K Patil and Prof (Ms).Vrushali G Nasre, “Wide-Frequency-Range Cmos

Voltage Controlled Oscillator for Phase Lock Loop – A Review” International journal

of Electronics and Communication Engineering &Technology (IJECET),

Volume 3, Issue 1, 2012, pp. 10-16, Published by IAEME.

[9] Praveer Saxena, Swati Dhamani, Dinesh Chandra, Sampath Kumar V, “Modified Two

Phases Drive Adiabatic Dynamic Cmos Logic” International journal of Electronics

and Communication Engineering &Technology (IJECET),Volume 3,Issue 2,

2012, pp. 141-147, Published by IAEME.

[10] Rajinder Tiwari, R. K. Singh, “An Innovative Approach of High Performance Cmos

Current Conveyor - Ii for Analog Signal Processing Applications” International

Journal of Computer Engineering & Technology (IJCET) Volume 3, Issue 1,

2012, pp 147-153, Published by IAEME



263

[11] Dhanisha N. Kapadia , Priyesh P. Gandhi, “Design And Simulation Of High Speed

Cmos Differential Current Sensing Comparator In 0.35 µm And 0.25µ Technologies”

International journal of Electronics and Communication Engineering

&Technology (IJECET),Volume 3,Issue 3, 2012, pp. 147-152, Published by

IAEME.

[12] Rajinder Tiwari, R K Singh, “an Optimized High Speed Dual Mode Cmos

Differential Amplifier for Analog Vlsiapplications” International Journal of Electrical

Engineering & Technology (IJEET) Volume 3, Issue 1, 2012, pp. 180-187,

Published by IAEME.

[13] P.Sreenivasulu, Krishnna veni, Dr. K.Srinivasa Rao,Dr.A.VinayaBabu, “Low Power

Design Techniques Of Cmos Digital Circuits” International journal of Electronics

and Communication Engineering &Technology (IJECET),Volume 3,Issue 2,


[14] Suhas. S. Khot, Prakash. W. Wani , Mukul. S. Sutaone and Saurabh.K.Bhise, “A

581/781 Msps 3-Bit Cmos Flash Adc Using Tiq Comparator” International journal of

Electronics and Communication Engineering &Technology (IJECET),Volume

3, Issue 2, 2012, pp. 352-359, Published by IAEME.

[15] S. S. Khot, P. W. Wani,M. S. Sutaone and S.K.Bhise, “A 555/690 Msps 4-Bit

Cmos Flash Adc Using Tiq Comparator” International journal of Electronics and

Communication Engineering &Technology (IJECET),Volume 3, Issue 2, 2012,

pp. 373-382, Published by IAEME.

[16] S. S. Khot, P. W. Wani, M. S. Sutaone and S.K.Bhise, “A Low Power 2.5 V, 5-Bit,

555-Mhz Flash Adc In 0.25µ Digital Cmos” International journal of Electronics and

Communication Engineering &Technology (IJECET),Volume 3, Issue 2,


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