Datasheet DW9255 Datasheet (MITEL)

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 centre­frequency 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°C

APPLICATION

■ Commercial Global Positioning

DW9255

DW9255

35.42MHz SAW Filter for GPS Receivers

DS3861 - 3.1 November 1997

INPUT+

21

GND

GND

GND

GND

GND

GND

GND

GND

3

4

DW9255

5

6

78

OUTPUT+

INPUT +

21

3

4

DW9255

5

6

12

11

10

9

OUTPUT- INPUT-

INPUT -

12

11

10

9

GND

GND

GND

GND

LCS12/1

GND

GND

GND

GND

RELATED PRODUCTS AND PUBLICATIONS

Part

GP2010
GP2015

Description

GPS receiver RF Front-end
Miniature GPS receiver

RF Front-end

Data

Reference

DS4056

DS4374

78

OUTPUT +

OUTPUT -

Fig.1 Pinout

LCS12/4

1

DW9255

GPS Antenna

SAW

1st IF Filter DW9255

LNA

GP2010/15

RF Front End

Clock

Crystal

GP2021

12 channel

Correlator

DATA BUS

+ Support
Functions

ADDRESS BUS

TCXO

2 x Serial

Communications Ports

(Programmable UARTS)

Fig.2 DW9255 used with GPS chipset

ELECTRICAL CHARACTERISTICS (Typ. @ 25°C)

Parameter Min Typ Max Units

TO
PROCESSOR

Centre Frequency - 35.42 - MHz
1dB Bandwidth 1.6 1.9 - MHz
Insertion Loss 16 17 18 dB
Amplitude Ripple - 0.8 1.6 dB (pk to pk)

(34.62 to 36.22MHz)
Relative Attenuation <28MHz 35 40 - dB

(relative to insertion loss) <31MHz 30 35 - dB

<33.5MHz 21 25 - dB
>37.5MHz 21 25 - dB
>40MHz 25 30 - dB
>50MHz 30 40 - dB
>63MHz 28 35 - dB
>73 - 110MHz 40 45 - dB

Group Delay Ripple - 190 300 ns
(34.62 to 36.22MHz)

Maximum Group Delay - 1.6 1.7 µs
(34.62 to 36.22MHz)

Operating Temperature Range -40 - +85 °C

2

DW9255 used as 2nd IF filter for GP2010/15

DW9255

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 500Ω typical
Load Impedance 1000Ω 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

5
0

-5

-10

-15

-20

than 20dB) beyond this bandwidth, and so should have a brick­wall 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.

-25

Insertion Loss (dB)

-30

-35

-40
32 33 34 35 36 37 38

FREQUENCY (MHz)

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

3

DW9255

VCC

L2L1

SOURCE

IMPEDANCE

= 500Ω

MIX

2

O/P

IP+

DW9255

IP-

GP2010

GP2010 or GP2015

OP+

OP-

2.2µH

COILCRAFT

1008

MIX

3

I/P

LOAD

IMPEDANCE

= 1KΩ

L1, L2 = 560nH COILCRAFT 1008

Fig.4 Typical matching components when used with GP2010 or GP2015 GPS Front-end IC

680nH

COILCRAFT 1008

IP+

OP+

910nF

COILCRAFT 1008

DW9255

15pF VITRAMON
(VJ0805A150JXA)

IP-

OP-

Pin 1 = IP­Pin 2 = IP+
Pin 7 = OP+
Pin 8 = OP-

Fig.5 50Ω Matching network

4

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