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TDA7338 데이터시트(PDF) 7 Page - STMicroelectronics |
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TDA7338 데이터시트(HTML) 7 Page - STMicroelectronics |
7 / 12 page 7/12 TDA7338 4.3.2 Noise Controlled Threshold Adjustment (ATC) The behaviour of the noise controlled threshold adjustment is shown in fig. 8. It can be influenced lightly by adding a resistor in parallel to the PEAK capacitor at Pin 8 either to GND or VDD. A resistor to GND will decrease the threshold whereas a resistor to VDD will increase it. But it is recommended to choose one of the internal thresholds by use of the PROG pin (see table 5) 4.3.3 Automatic Threshold Control by the Stereoblend voltage (ATC-SB) Besides the noise controlled threshold adjustment there is an additional possibility for influencing the trig- ger. It is controlled by the difference between Vsb and Vr, similar to the Stereoblend. The reason for im- plementing such a second control will be explained in the following: The point where the MPX signal starts to become noisy is fixed by the RF part. Therefore also the starting point of the normal noise controlled trigger adjustment is fixed (fig.9). But in some cases the behaviour of the noiseblanker can be improved by increasing the threshold even in a region of higher fieldstrength, for the MPX signal often shows distor- tion in this range, which leads to an undesired triggering. Because of the overlap of this range and the range of the stereo/mono transition it can be controlled by Vsb and Vr. This threshold increase is programmable (see fig. 9). 4.3.4 Blend Mode Another possibility to avoid a disturbing triggering on modulation is to use the spikes on the fieldstrength signal (LEVEL pin). But in the range of higher fieldstrength the signal saturates and no more spike detec- tion is possible. For this reason the TDA7338 offers the "BLEND MODE". When "BLEND MODE" is acti- vated a smooth transition between the LEVEL- and the MPX-signal is used to detect the spikes either on LEVEL or on MPX. In the lower fieldstrength range mainly the LEVEL-signal is used whereas in the higher range mainly the MPX is used. This switching is controlled also by the normal Stereoblend signal to avoid additional pins. "BLEND MODE OFF" is activated by connecting the LEVEL pin to GND (LEVEL must be also connected to GND if not used). Figure 7. Block Diagram of the Noise Blanker 80KHz LP SIGNAL PATH ATC AUTOMATIC THRESHOLD CONTROL PEAK+VTH RECT-PEAK BUF PEAK AMP RECT PEAK COMP REF. BLANK COMP ADDITIONAL THRESHOLD CONTROL (ATC-SB) 40 µs LEFT RIGHT to OUTPUTS MPX IN VR VSB CPEAK 47nF CBLANK 330pF D95AU368 140KHz HP 120KHz HP LEVEL 2V 7V THRESHOLD L/H ADDITIONAL THRESHOLD CONTROL on/off PROG VS - + BLEND ON/OFF 0.1V BLEND CONTROL |
유사한 부품 번호 - TDA7338_05 |
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유사한 설명 - TDA7338_05 |
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