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MC13173FTB データシート(PDF) 5 Page - Motorola, Inc |
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MC13173FTB データシート(HTML) 5 Page - Motorola, Inc |
5 / 18 page MC13173 5 MOTOROLA ANALOG IC DEVICE DATA Master VCO/PLL The master VCO provides the reference frequency for the FSK modulator and the LO frequency for the receiver downconverter. With a 32.768 kHz input frequency to the master VCO on Pin 1, the LO frequency for the receiver will be at 12.075 MHz. The reference frequency for the FSK modulator will be at approximately 1.1 MHz. The master VCO and FSK modulator are not used when the transmitter is used in A/V mode, and both are powered down. Receiver Description The single conversion receiver portion of the MC13173 is low power and wideband, and incorporates a split IF. This section includes a mixer, IF amplifier, limiting IF, quadrature detector and data slicer. Mixer The mixer is a double balanced four quadrant multiplier. It can be driven either differentially or single–ended by connecting the unused input to the positive supply rail. The buffered output is internally loaded for an output impedance of 330 Ω for use with a standard ceramic filter. IF Amplifier The first IF amplifier section is composed of three differential stages with the second and third stages contributing to the RSSI. This section has internal DC feedback and external input decoupling for improved symmetry and stability. The total gain of the IF amplifier block is approximately 40 dB. The fixed internal input impedance is 330 Ω for use with a 10.7 MHz ceramic filter. The output of the IF amplifier is buffered and the impedance is 330 Ω. Limiter The limiter section is similar to the IF amplifier section, except that four stages are used with the last three contributing to the RSSI. This IF limiting amplifier section drives the quadrature detector internally. RSSI/Carrier Detect The received signal strength indicator (RSSI) outputs a current proportional to the log of the received signal amplitude. The RSSI current output is derived by summing the currents from the IF and limiting amplifier stages. An external resistor sets the output voltage range. The carrier detect threshold is set at approximately 1.2 Vdc. When the RSSI level exceeds that threshold, the carrier detect output will go high. A large resistor may be added externally between the comparator output and the positive input for hysteresis. Quadrature Detector The demodulator is a conventional quadrature type with an external LC tank driven through an internal 5 pF capacitor. The output is buffered to give an output impedance of less than 1.0 k Ω at an average DC level of around 1.1 V. Data Slicer The data slicer is designed to square up the data signal. It is self centering at about 1.1 V, and clips at about 0.75 V and 1.45 V. There is a short time constant for large peak–to–peak voltage swings or when there is a change in DC level at the detector output. The time constant is longer for small signals or for continuous bits of the same polarity which drift close to the threshold voltage. Transmission Description The MC13173 uses a dual modulus PLL to frequency shift key (FSK) modulate the baseband digital input signal, producing the necessary logic high and low frequencies for transmission. The transmit frequency for a logic high is 1.427 MHz, and the frequency for a low is 1.317 MHz with a 32.768 kHz reference frequency. FSK Modulator In the communications mode, the FSK modulator uses the reference frequency from the Master VCO to produce the two frequencies required for a logic high and a logic low. In the A/V mode, the FSK modulator is not used and is powered down. LED Driver Stage A low pass filter following the FSK modulator removes the undesired harmonic frequencies from the square–wave output of the divider circuits in PLLs. The resulting sinusoidal waveforms are fed into a unity gain difference amplifier, which drives the base of an external transistor, modulating the IR LED. In A/V mode, the data is input directly into the inverting input of the op amp, and the low pass filter is not used. |
同様の部品番号 - MC13173FTB |
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同様の説明 - MC13173FTB |
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