DW9255 DW9255 35.42MHz SAW Filter for GPS Receivers GND 3 GND 4 INPUT- 2 1 12 GND 11 GND DW9255 5 10 GND GND 6 9 GND 7 8 OUTPUT- GND OUTPUT+ 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. INPUT+ DS3861 - 3.1 November 1997 LCS12/1 ■ Insertion Loss of 17dB ±1dB (typical) ■ 1dB Bandwidth 1.9MHz (typical) INPUT - ■ Centre Frequency of 35.42MHz INPUT + FEATURES 2 1 ■ Passband Ripple 0.8dB (typical) ■ Low Profile Ceramic Surface Mount Package ■ Operating Temperature Range -40° to +85°C GND 3 12 GND GND 4 11 GND DW9255 5 10 GND GND 6 9 GND ■ Commercial Global Positioning RELATED PRODUCTS AND PUBLICATIONS Part Description Data Reference GP2010 GPS receiver RF Front-end DS4056 GP2015 Miniature GPS receiver RF Front-end DS4374 7 8 OUTPUT - GND OUTPUT + APPLICATION LCS12/4 Fig.1 Pinout 1 DW9255 GPS Antenna SAW 1st IF Filter Clock Crystal DW9255 LNA GP2021 12 channel Correlator + Support Functions GP2010/15 RF Front End DATA BUS 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 - 35.42 - MHz 1dB Bandwidth 1.6 1.9 - MHz Insertion Loss 16 17 18 dB - 0.8 1.6 dB (pk to pk) 35 30 21 21 25 30 28 40 40 35 25 25 30 40 35 45 - dB dB dB dB dB dB dB dB Group Delay Ripple (34.62 to 36.22MHz) - 190 300 ns Maximum Group Delay (34.62 to 36.22MHz) - 1.6 1.7 µs -40 - +85 °C Centre Frequency Amplitude Ripple (34.62 to 36.22MHz) Relative Attenuation <28MHz (relative to insertion loss) <31MHz <33.5MHz >37.5MHz >40MHz >50MHz >63MHz >73 - 110MHz Operating Temperature Range 2 TO PROCESSOR DW9255 DW9255 used as 2nd IF filter for GP2010/15 Centre Frequency Pass Band Insertion loss 3rd IF Image frequency at 2nd IF Source Impedance Load Impedance 35.42MHz ±1.0MHz (within ±1.0dB) 14-18dB 26.8MHz 500Ω typical 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 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. 5 Insertion Loss (dB) 0 - 5 -10 -15 -20 -25 -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 L1 L2 IP+ SOURCE IMPEDANCE = 500Ω MIX 2 O/P OP+ DW9255 IP- MIX 3 I/P 2.2µH LOAD IMPEDANCE = 1KΩ OPCOILCRAFT 1008 GP2010 GP2010 or GP2015 L1, L2 = 560nH COILCRAFT 1008 Fig.4 Typical matching components when used with GP2010 or GP2015 GPS Front-end IC 680nH 910nF IP+ OP+ COILCRAFT 1008 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 http://www.mitelsemi.com World Headquarters - Canada Tel: +1 (613) 592 2122 Fax: +1 (613) 592 6909 North America Tel: +1 (770) 486 0194 Fax: +1 (770) 631 8213 Asia/Pacific Tel: +65 333 6193 Fax: +65 333 6192 Europe, Middle East, and Africa (EMEA) Tel: +44 (0) 1793 518528 Fax: +44 (0) 1793 518581 Information relating to products and services furnished herein by Mitel Corporation or its subsidiaries (collectively “Mitel”) is believed to be reliable. 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