DW9255

The DW9255 is a Surface Acoustic Wave (SAW) bandpass

filter for use with the GP2000 Global Positioning System
(GPS) receiver chip-set, available from Mitel Semiconductor.
It is pre-tuned to the exact 2nd IF filter requirements of the
GP2010 & GP2015 RF front-end devices, with a centre-
frequency of 35.42MHz. The response is tuned for a flat
passband, steep stopband and uniform passband group-delay
with 3 external inductors. The device is realised on a Lithium
Tantalate substrate and housed in a small leadless ceramic
Surface Mount package.

The DW9255 gives significant improvement in correlated

GPS Signal-to-Noise Ratio (SNR) performance compared to
conventional LC bandpass filter schemes. This aids satellite
signal acquisition and tracking capability from the GP2000
GPS chip-set. This device effectively filters out-of-band
(unwanted) noise in the GPS signal. The Automatic Gain
Control (AGC) within the GP2010 and GP2015 RF Front-end
devices will then operate only on in-band noise for optimum
gain and superior correlated GPS signal strength.

FEATURES

Centre Frequency of 35.42MHz

Insertion Loss of 17dB

1dB (typical)

1dB Bandwidth 1.9MHz (typical)

Passband Ripple 0.8dB (typical)

Low Profile Ceramic Surface Mount Package

Operating Temperature Range -40

to +85

APPLICATION

Commercial Global Positioning

Fig.1 Pinout

GND

DW9255

LCS12/1

OUTPUT+

OUTPUT-

INPUT-

INPUT+

Description

GPS receiver RF Front-end

Miniature GPS receiver
RF Front-end

RELATED PRODUCTS AND PUBLICATIONS

Part

GP2010

GP2015

Data

Reference

DS4374

DS4056

INPUT -

INPUT +

OUTPUT +

OUTPUT -

GND

DW9255

LCS12/4

DW9255

35.42MHz SAW Filter for GPS Receivers

DS3861 - 3.1 November 1997

DW9255

ELECTRICAL CHARACTERISTICS (Typ. @ 25

Parameter

Min

Typ

Max

Units

Centre Frequency

35.42

MHz

1dB Bandwidth

1.6

1.9

MHz

Insertion Loss

Amplitude Ripple

0.8

1.6

dB (pk to pk)

(34.62 to 36.22MHz)

Relative Attenuation

<28MHz

(relative to insertion loss) <31MHz

<33.5MHz

>37.5MHz

>40MHz

>50MHz

>63MHz

>73 - 110MHz

Group Delay Ripple

190

300

(34.62 to 36.22MHz)

Maximum Group Delay

1.6

1.7

(34.62 to 36.22MHz)

Operating Temperature Range

-40

+85

Fig.2 DW9255 used with GPS chipset

1st IF Filter

DW9255

GP2010/15

RF Front End

GP2021

12 channel

Correlator

+ Support
Functions

Clock

Crystal

TCXO

GPS Antenna

SAW

LNA

2 x Serial

Communications Ports

(Programmable UARTS)

DATA BUS

ADDRESS BUS

TO
PROCESSOR

DW9255

DW9255 used as 2nd IF filter for GP2010/15

Centre Frequency

35.42MHz

Pass Band

1.0MHz (within

1.0dB)

Insertion loss

14-18dB

3rd IF Image frequency at 2nd IF

26.8MHz

Source Impedance

500

typical

Load Impedance

1000

typical

The second external IF filter is connected between the output
of Stage 2 and input of Stage 3. It is required to define the
bandwidth of the RF section of the GPS receiver, hence it is
critical to the receiver performance. The filter should be flat
across the 2MHz bandwidth of the GPS Coarse-Acquisition
(C/A) code signal. It should also have high rejection (greater

than 20dB) beyond this bandwidth, and so should have a brick-
wall type response at these extremes. The DW9255 SAW
filter provides a 1dB Bandwidth of typically 1.9MHz centred on
35.42MHz, with a typical pass band ripple of 0.8dB, when the
SAW input and output capacitance is resonantly matched with
inductors of optimum value. The out-of-band signal rejection is
better than 21dB at

2.0MHz, and better than 35dB at

7.5MHz.

The frequency response of the DW9255 SAW filter with
matching components is shown in Fig. 3. The matching
components used with the GP2010/15 device are shown in
Fig. 4.

Fig.3 Typical frequency response of DW9255 SAW filter used as 2nd IF filter

- 4 0

- 3 5

- 3 0

- 2 5

- 2 0

- 1 5

- 1 0

- 5

3 2

3 3

3 4

3 5

3 6

3 7

3 8

FREQUENCY (MHz)

Insertion Loss (dB)

TECHNICAL DOCUMENTATION - NOT FOR RESALE

World Headquarters - Canada

Tel: +1 (613) 592 2122

Fax: +1 (613) 592 6909

North America

Asia/Pacific

Europe, Middle East,

Tel: +1 (770) 486 0194

Tel: +65 333 6193

and Africa (EMEA)

Fax: +1 (770) 631 8213

Fax: +65 333 6192

Tel: +44 (0) 1793 518528

Fax: +44 (0) 1793 518581

http://www.mitelsemi.com

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