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NE570 Datasheet(PDF) 4 Page - ON Semiconductor |
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NE570 Datasheet(HTML) 4 Page - ON Semiconductor |
4 / 10 page NE570 http://onsemi.com 4 13 2, 15 4 1, 16 5, 12 8, 9 7, 10 6, 11 V1 V2 VO VCC = 15 V VREF 10 mF 0.1 mF 200 pF 8.2 k W 2.2 mF − + 30 k W 20 k W DG 10 k W 20 k W 2.2 mF 3, 14 2.2 mF Figure 3. Typical Test Circuit INTRODUCTION Much interest has been expressed in high performance electronic gain control circuits. For non−critical applications, an integrated circuit operational transconductance amplifier can be used, but when high−performance is required, one has to resort to complex discrete circuitry with many expensive, well−matched components. This paper describes an inexpensive integrated circuit, the NE570 Compandor, which offers a pair of high performance gain control circuits featuring low distortion (<0.1 %), high signal−to−noise ratio (90 dB), and wide dynamic range (110 dB). CIRCUIT BACKGROUND The NE570 Compandor was originally designed to satisfy the requirements of the telephone system. When several telephone channels are multiplexed onto a common line, the resulting signal−to−noise ratio is poor and companding is used to allow a wider dynamic range to be passed through the channel. Figure 4 graphically shows what a compandor can do for the signal−to−noise ratio of a restricted dynamic range channel. The input level range of +20 dB to −80 dB is shown undergoing a 2−to−1 compression where a 2.0 dB input level change is compressed into a 1.0 dB output level change by the compressor. The original 100 dB of dynamic range is thus compressed to a 50 dB range for transmission through a restricted dynamic range channel. A complementary expansion on the receiving end restores the original signal levels and reduces the channel noise by as much as 45 dB. The significant circuits in a compressor or expander are the rectifier and the gain control element. The phone system requires a simple full−wave averaging rectifier with good accuracy, since the rectifier accuracy determines the (input) output level tracking accuracy. The gain cell determines the distortion and noise characteristics, and the phone system specifications here are very loose. These specs could have been met with a simple operational transconductance multiplier, or OTA, but the gain of an OTA is proportional to temperature and this is very undesirable. Therefore, a linearized transconductance multiplier was designed which is insensitive to temperature and offers low noise and low distortion performance. These features make the circuit useful in audio and data systems as well as in telecommunications systems. INPUT LEVEL OUTPUT LEVEL NOISE +20 0 dB −40 −80 −20 0 dB −40 −80 Figure 4. Restricted Dynamic Range Channel |
Similar Part No. - NE570_06 |
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Similar Description - NE570_06 |
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