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MC13142D Scheda tecnica(PDF) 8 Page - Motorola, Inc |
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MC13142D Scheda tecnica(HTML) 8 Page - Motorola, Inc |
8 / 16 page MC13142 8 MOTOROLA RF/IF DEVICE DATA Input Matching/Components It is desirable to use a RF ceramic or SAW filter before the mixer to provide image frequency rejection. The filter is selected based on cost, size and performance tradeoffs. Typical RF filters have 3.0 to 5.0 dB insertion loss. The PC board layout accommodates both ceramic and SAW RF filters which are offered by various suppliers such as Siemens, Toko and Murata. Interface matching between the LNA, RF filter and the mixer will be required. The interface matching networks shown in the application circuit are designed for 50 Ω interfaces. In the application circuit, the LNA is conjugately matched to 50 Ω input and output for 3.0 to 5.0 Vdc VCC. 17 dB gain and 1.8 dB noise figure is typical at 926 MHz. The mixer measures 0 dB gain and 12 dB noise figure as shown in the application circuit. Typical insertion loss of the Toko ceramic filter is 3.0 dB. Thus, the overall gain of the frontend receiver is 14 dB with a 3.3 dB noise figure. System Noise Considerations The block diagram shows the cascaded noise stages of the MC13142 in the frontend receiver subsystem; it represents the application circuit. In the cascaded noise analysis the system noise equation is: Fsystem = F1 + [(F2 –1)/G1] + [(F3–1)]/[(G1)(G2)] where: F1 = the Noise Factor of the MC13142 LNA G1 = the Gain of the LNA F2 = the Noise factor of the RF Ceramic Filter G2 = the Gain of the Ceramic Filter F3 = the Noise factor of the Mixer Note: the above terms are defined as linear relationships and are related to the log form for gain and noise figure by the following: F = Log –1 [(NF in dB)/10] and similarly G = Log –1 [(Gain in dB)/10]. Calculating in terms of gain and noise factor yields the following: F1 = 1.51; G1 = 50.11 F2 = 1.99; G2 = 0.5 F3 = 15.85 Thus, substituting in the equation for system noise factor: Fsystem = 2.12; NFsystem = 3.3 dB Figure 3. Frontend Subsystem Block Diagram for Noise Analysis fLO = 975.55 MHz Noise Source IF Output Toko Ceramic Filter NF Meter 330 nH VCC Mixer Local Oscillator G1 = 17 dB NF1 = 1.8 dB 36 p fIF = 49.05 MHz Z Transformer 16:1 G2 = –3.0 dB NF2 = 3.0 dB LNA G3 = 0 dB NF3 = 12 dB Gsys = 14 dB NFsys = 3.3 dB fRF = 926.5 MHz |
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