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MC13027P Datasheet(PDF) 6 Page - Motorola, Inc |
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MC13027P Datasheet(HTML) 6 Page - Motorola, Inc |
6 / 28 page MC13027 MC13122 6 MOTOROLA ANALOG IC DEVICE DATA AMAX STEREO CHIPSET What is AMAX? In 1993, a joint proposal by the EIA (Electronic Industries Association) and the NAB (National Association of Broadcasters) was issued. It included a unified standard for pre–emphasis and distortion for broadcasters as well as a set of criteria for the certification of receivers. The purpose of this proposal was to restore quality and uniformity to the AM band and to make it possible for the consumer to receive high quality signals using the AM band. The FCC has been supportive of this initiative and has required all new broadcast licensees to meet AMAX standards. The NAB and EIA have continued to encourage receiver manufacturers by offering the AMAX certification logo to be displayed on all qualifying radios. This logo is shown below. or The Receiver Criteria An AMAX receiver must have wide bandwidth: 7.5kHz for home and auto, 6.5 kHz for portables. It must have some form of bandwidth control, either manual or automatic, including at least two bandwidth provisions, such as “narrow” and “wide”. It must meet NRSC receiver standards for distortion and deemphasis. It must have provisions for an external antenna. It must be capable of tuning the expanded AM band (up to 1700 kHz). And finally, home and auto receivers must have effective noise blanking. All of these requirements, except the noise blanking, have been met by Motorola’s previous AM radio products, such as MC13025 Front End and the MC13022A C–QUAM stereo decoder. It is the Noise Blanker requirement which is met by the two devices on this data sheet, the MC13027 and MC13122. Noise blanking, especially in AM auto radios, has become extremely important. The combination of higher energy ignitions, using multiple spark coils, along with increased use of plastic in the auto body, have increased the noise energy at the radio. Also, the consumer has learned to expect higher quality audio due to advances in many other media. For the AM band to sustain interest to the consumer, a truly effective noise blanker is required. The block diagram below shows the Motorola AMAX stereo chipset. It offers a two–pronged approach to noise blanking which is believed to be the most effective yet offered in the consumer market. The initial blanking takes place in the output of the mixer, using a shunt circuit triggered by a carefully defined wideband receiver. For most noises, some residual audible disturbance is almost always still present after this process. The disturbance becomes stretched and delayed as it passes through the rest of the selectivity in the receiver. The stretching and delay are predictable, so the MC13027 can provide a noise blanking pulse with the correct delay and stretch to the output stages of the MC13122 decoder. The MC13122 has a Track and Hold circuit which receives the blanking signal from the Front End and uses it to gently hold the audio wherever it is as the pulse arrives, and hold that value until the noise has passed. The combined effect is dramatic. A wide range of types of noise is successfully suppressed and the resulting audio seems almost clean until the noise is so intense that the blanking approaches full–time. The amount of extra circuitry to accomplish noise blanking is relatively small. The external components for this added capability are shown in Figure 3. In the MC13027 Front end, the noise receiver/detector requires two capacitors. The presettings for blanking timing and blanking delay require three external fixed resistors. Finally the decoder requires two track and hold capacitors to store the “audio” voltage during the track and hold function. Figure 3. AMAX Stereo Receiver with Noise Blanker MC13027 MC13122 Audio Blank 450 kHz Filter RF Attenuate Left Right RF In Pin Diode Reset AGC RF Amplifier Mixer IF Amplifier AGC’d IF Amplifier AM Stereo Decoder Track and Hold Variable Notch Filter Wideband AGC 4.0 V Regulator Divide by 4 VCO RF Attenuator Switch RF Blank Timer AGC’d RF Amplifier AM Detector Audio Reject Filter Pulse Detector Delay Timer Audio Blank Timer Audio Blank Switch |
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