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MC3335 bảng dữ liệu(PDF) 4 Page - Motorola, Inc |
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MC3335 bảng dữ liệu(HTML) 4 Page - Motorola, Inc |
4 / 6 page MC3335 4 MOTOROLA ANALOG IC DEVICE DATA CIRCUIT DESCRIPTION The MC3335 is a complete FM narrowband receiver from antenna input to audio preamp output. The low voltage dual conversion design yields low power drain, excellent sensitivity and good image rejection in narrowband voice and data link applications. In the typical application diagram, the first mixer amplifies the signal and converts the RF input to 10.7 MHz. This IF signal is filtered externally and fed into the second mixer, which further amplifies the signal and converts it to a 455 kHz IF signal. After external bandpass filtering, the low IF is fed into the limiting amplifier and detection circuitry. The audio is recovered using a conventional quadrature detector. Twice–IF filtering is provided internally. The input signal level is monitored by meter drive circuitry which detects the amount of limiting in the limiting amplifier. The voltage at the meter drive pin determines the state of the carrier detect output which is active low. APPLICATIONS INFORMATION The first local oscillator can be run using a free running LC tank, as a VCO using PLL synthesis, or driven from an external crystal oscillator. At higher VCC values (6.0 to 7.0 V), it has been run to 170 MHz. The second local oscillator is a common base Colpitts type which is typically run at 10.245 MHz under crystal control. The mixers are doubly balanced to reduce spurious responses. The first and second mixers have conversion gains of 18 dB and 22 dB (typical), respectively. Mixer gain is stable with respect to supply voltage. For both conversions, the mixer impedances and pin layout are designed to allow the user to employ low cost, readily available ceramic filters. Overall sensitivity is shown in Figure 5. The input level for 20 dB (S + N)/N is 1.3 µV using the two–pole post–detection filter as demonstrated. Following the first mixer, a 10.7 MHz ceramic bandpass filter is recommended. The 10.7 MHz filtered signal is then fed into one second mixer input pin, the other input pin being connected to VCC. Pin 5 (VCC) is treated as a common point for emitter–driven signals. The 455 kHz IF is typically filtered using a ceramic bandpass filter, then fed into the limiter input pin. The limiter has 10 µV sensitivity for –3.0 dB limiting, flat to 1.0 MHz. The output of the limiter is internally connected to the quadrature detector, including a quadrature capacitor. A parallel LC tank is needed externally from Pin 11 to VCC. A 39 k Ω shunt resistance is included which determines the peak separation of the quadrature detector; a smaller value will increase the spacing and linearity but decrease recovered audio and sensitivity. A data shaping circuit is available and can be coupled to the recovered audio output of Pin 12. The circuit is a comparator which is designed to detect zero crossings of FSK modulation. Data rates of up to 35000 baud are detectable using the typical application. Hysteresis is available by connecting a high–valued resistor from Pin 13 to Pin 14. Values below 120 k Ω are not recommended as the input signal cannot overcome the hysteresis. The meter drive circuitry detects input signal level by monitoring the limiting of the limiting amplifier stages. Figure 2 shows the unloaded current at Pin 9 versus input power. The meter drive current can be used directly (RSSI) or can be used to trip the carrier detect circuit at a specified input power. To do this, pick an RF trip level in dBm. Read the corresponding current from Figure 2 and pick a resistor such that: R9 = 0.64 Vdc / I9 Hysteresis is available by connecting a high–valued resistor RH between Pin 9 and 10. The formula is: Hysteresis = VCC/(RH x 10–7) dB |
Số phần tương tự - MC3335 |
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Mô tả tương tự - MC3335 |
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