BAF :. The is a mute detector designed for car stereos. It low external parts count, and can detect mute whether the tape is playing or being fast-forwarded. It a wide power supply voltage range to

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It is intended for quality receivers produced in large quantities. Test circuit Figure 2. Audio output, noise and tweet levels vs. Distortion vs. Audio output vs. Audio output and noise level vs. Amplitude modulation rejection vs. DC output voltage pin. DC output voltage p i n 9 vs. Bias is provided at pin 4 which must be adequately decoupled. The RF amplifier provides stable performance extending beyond 30 MHz.

The Mixer employed is a double - balanced multiplier and the IF output at pin 3 is connected directly to the IF filter coil. Local oscillator The local oscillator is a cross coupled differential stage which oscillates at the frequency determined by the load on pin 1. The oscillator resonant circuit is transformer coupled to pin 1 to improve the Q factor and frequency stability. An external oscillator can be injected at pin 1. The level should be 50 mV rms and pin 1 should be connected to the supply via a W resistor.

AM detection occurs at pin 7. A detection capacitor is connected to pin 6 to reduce the radiation of spurious detector products. The audio output impedance is about 7K? AGC Automatic gain control operates in two ways. At pin 8 there is a carrier envelope signal which is filtered by an external capacitor to remove the Audio and RF content and obtain a mean DC signal to drive the AGC circuit. Pin 16 is the amplifier input and has a typical input impedance of 6.

Pin 15 is the second input to the amplifier and is decoupled to pin 14, which is grounded by a 20 nF capacitor. The signal level at pin 13 is about mV rms FM Detector The circuit uses a quadrature detector and the choise of component values is determined by the acceptable level of distortion at a given recovered audio level.

With a double tuned network the linearity improves distortion is reduced and the phase shift can be optimized; however this leads to a reduction in the level of the recovered audio. A satisfactory compromise for most FM receiver applications is shown in the test circuit. Care shoul be taken with the physical layout.

The main recommandations are:? Locate the phase shift coil as near as possible to pin Shunt pins 14 and 16 with a low value resistor between 56?

Ground the decoupling capacitor of pin 14 and the PC board and component layout of the fig. CORE: 10x80 mm. Low cost 27 MHz receiver Figure L2 Oscillator coil Figure Secondary winding: 4 Turns copper wire 0. Discriminator "S" curve response circuit of fig. However, SGS-THOMSON Microelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use.

Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied.


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