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Datenblatt-Suchmaschine für elektronische Bauteile |
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Datenblatt-Suchmaschine für elektronische Bauteile |
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MC13175 Datenblatt(PDF) 10 Page - Motorola, Inc |
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MC13175 Datenblatt(HTML) 10 Page - Motorola, Inc |
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10 / 17 page  MC13175 MC13176 10 MOTOROLA RF/IF DEVICE DATA Figure 16 shows the improved hold–in range of the loop. The ∆fref is moved 950 kHz with over 200 µA swing of control current for an improved hold–in range of ±15.2 MHz or ± 95.46 Mrad/sec. Figure 16. MC13176 Reference Oscillator Frequency versus Oscillator Control Current –150 I6, OSCILLATOR CONTROL CURRENT (µA) –100 – 50 50 100 0 Closed Loop Response: fo = 32 x fref VCC = 3.0 Vdc ICC = 38 mA Pout = 4.8 dB Imod = 2.0 mA Vref = 500 mVp–p 10.6 10.4 10.2 9.6 9.4 10 9.8 Lock–in Range/Capture Range If a signal is applied to the loop not equal to free running frequency, ff, then the loop will capture or lock–in the signal by making fs = fo (i.e. if the initial frequency difference is not too great). The lock–in range can be expressed as ∆ωL ~ ± 2∂ωn FM Modulation Noise external to the loop (phase detector input) is minimized by narrowing the bandwidth. This noise is minimal in a PLL system since the reference frequency is usually derived from a crystal oscillator. FM can be achieved by applying a modulation current superimposed on the control current of the CCO. The loop bandwidth must be narrow enough to prevent the loop from responding to the modulation frequency components, thus, allowing the CCO to deviate in frequency. The loop bandwidth is related to the natural frequency ωn. In the lag–lead design example where the natural frequency, ωn = 5.0 krad/sec and a damping factor, ∂ = 0.707, the loop bandwidth = 1.64 kHz. Characterization data of the closed loop responses for both the MC13175 and MC13176 at 320 MHz (Figures 7 and 8, respectively) show satisfactory performance using only a simple low–pass loop filter network. The loop filter response is strongly influenced by the high output impedance of the push–pull current output of the phase detector. = 0.159/RC; = 1.0 k + R7 (R7 = 53 k) and C = 390 pF = 7.55 kHz or ωc = 47 krad/sec fc For R fc The application example in Figure 18 of a 320 MHz FM transmitter demonstrates the FM capabilities of the IC. A high value series resistor (100 k) to Pin 6 sets up the current source to drive the modulation section of the chip. Its value is dependent on the peak to peak level of the encoding data and the maximum desired frequency deviation. The data input is AC coupled with a large coupling capacitor which is selected for the modulating frequency. The component placements on the circuit side and ground side of the PC board are shown in Figures NO TAG and NO TAG, respectively. Figure 20 illustrates the input data of a 10 kHz modulating signal at 1.6 Vp–p. Figures 21 and 22 depict the deviation and resulting modulation spectrum showing the carrier null at – 40 dBc. Figure 23 shows the unmodulated carrier power output at 3.5 dBm for VCC = 3.0 Vdc. For voice applications using a dynamic or an electret microphone, an op amp is used to amplify the microphone’s low level output. The microphone amplifier circuit is shown in Figure 17. Figure 19 shows an application example for NBFM audio or direct FSK in which the reference crystal oscillator is modulated. 120k 100k VCC MC33171 1.0 10k Electret Microphone 10k 3.9k Data Input Data or Audio Output Voice Input VCC 1.0k 3.3k Figure 17. Microphone Amplifier Local Oscillator Application To reduce internal loop noise, a relatively wide loop bandwidth is needed so that the loop tracks out or cancels the noise. This is emphasized to reduce inherent CCO and divider noise or noise produced by mechanical shock and environmental vibrations. In a local oscillator application the CCO and divider noise should be reduced by proper selection of the natural frequency of the loop. Additional low pass filtering of the output will likely be necessary to reduce the crystal sideband spurs to a minimal level. |
Ähnliche Teilenummer - MC13175 |
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Ähnliche Beschreibung - MC13175 |
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