DW9255

3

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

Ω typical

Load Impedance

1000

Ω 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

-40

-35

-30

-25

-20

-15

-10

-5

0

5

32

33

34

35

36

37

38

FREQUENCY (MHz)