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MC13022AP Scheda tecnica(PDF) 4 Page - Motorola, Inc |
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MC13022AP Scheda tecnica(HTML) 4 Page - Motorola, Inc |
4 / 8 page MC13022A 4 MOTOROLA ANALOG IC DEVICE DATA EXPLANATION OF FEATURES Blend and Noise Reduction Although AM stereo does not have the extreme difference in S/N between mono and stereo that FM does (typically less than 3.0 dB versus greater than 20 dB for FM), sudden switching between mono and stereo is quite apparent. Some forms of interference such as co–channel have a large L–R component that makes them more annoying than would ordinarily be expected for the measured level. The MC13022A measures the interference level and reduces L–R as interference increases, blending smoothly to monaural. The pilot indicator remains on as long as a pilot signal is detected, even when interference is severe, to minimize annoying pilot light flickering. Signal Strength A dc voltage proportional to the log of signal strength is provided at Pin 6. This can be used for signal strength indication, and it directly controls the post detection filter. Normal operation is above 2.2 V as shown is Figure NO TAG. Stop Sense The signal strength information is multiplexed with the stop sense signal. The stop sense is activated when scanning by externally pulling the blend, Pin 23, below 0.3 V. This would typically be done from the mute line in a frequency synthesizer. If at any time Pin 23 is low and there is either no signal in the IF or a noisy signal of a predetermined interference level, Pins 6 and 15 will go low. This low can be used to tell the frequency synthesizer to immediately scan to the next channel. The interference detection prevents stopping on many unlistenable stations, a feature particularly useful at night when many frequencies may have strong signals from multiple co–channel stations. Pin 6 drives a comparator which has a 1.7 V reference. Therefore the comparator output, Pin 15, is low if Pin 6 is <1.7 V and high if Pin 6 is >1.7 V. IF Bandwidth Control IF AGC attenuates the signal by shunting the signal at the IF input. This widens the IF bandwidth by decreasing the loaded Q of the input coupling coil as signal strength increases. Post Detection Filtering With weak, noisy signals, high frequency rolloff greatly improves the sound. Conventional tone controls do not attenuate the highs sufficiently to control noise without also significantly affecting the mid–range. Also, notch filters are necessary with any wide–band AM radio to eliminate the 10 kHz whistle from adjacent stations. By using a twin–T filter with variable feedback to the normally grounded center leg, a variable Q notch filter is formed that provides both the 10 kHz notch and variable high frequency rolloff functions. Typical range of response is shown in Figure NO TAG. Response is controlled by Pin 6 for automatic audio bandwidth control as a function of signal strength. |
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