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SA575N Datasheet(PDF) 4 Page - ON Semiconductor |
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SA575N Datasheet(HTML) 4 Page - ON Semiconductor |
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4 / 16 page  SA575 http://onsemi.com 4 Functional Description This section describes the basic subsystems and applications of the SA575 Compandor. More theory of operation on compandors can be found in AND8159 and AND8160. The typical applications of the SA575 low voltage compandor in an Expandor (1:2), Compressor (2:1) and Automatic Level Control (ALC) function are explained. These three circuit configurations are shown in Figures 2, 3, and 4 respectively. The SA575 has two channels for a complete companding system. The left channel, A, can be configured as a 1:2 Expandor while the right channel, B, can be configured as either a 2:1 Compressor, a 1:2 Expandor or an ALC. Each channel consists of the basic companding building blocks of rectifier cell, variable gain cell, summing amplifier and VREF cell. In addition, the SA575 has two additional high performance uncommitted op amps which can be utilized for application such as filtering, pre-emphasis/ de-emphasis or buffering. Figure 5 shows the complete schematic for the applications demo board. Channel A is configured as an expandor while channel B is configured so that it can be used either as a compressor or as an ALC circuit. The switch, S1, toggles the circuit between compressor and ALC mode. Jumpers J1 and J2 can be used to either include the additional op amps for signal conditioning or exclude them from the signal path. Bread boarding space is provided for R1, R2, C1, C2, R10, R11, C10 and C11 so that the response can be tailored for each individual need. The components as specified are suitable for the complete audio spectrum from 20 Hz to 20 kHz. The most common configuration is as a unity gain non-inverting buffer where R1, C1, C2, R10, C10 and C11 are eliminated and R2 and R11 are shorted. Capacitors C3, C5, C8, and C12 are for DC blocking. In systems where the inputs and outputs are AC coupled, these capacitors and resistors can be eliminated. Capacitors C4 and C9 are for setting the attack and release time constant. C6 is for decoupling and stabilizing the voltage reference circuit. The value of C6 should be such that it will offer a very low impedance to the lowest frequencies of interest. Too small a capacitor will allow supply ripple to modulate the audio path. The better filtered the power supply, the smaller this capacitor can be. R12 provides DC reference voltage to the amplifier of channel B. R6 and R7 provide a DC feedback path for the summing amp of channel B, while C7 is a short-circuit to ground for signals. C14 and C15 are for power supply decoupling. C14 can also be eliminated if the power supply is well regulated with very low noise and ripple. Demonstrated Performance The applications demo board was built and tested for a frequency range of 20 Hz to 20 kHz with the component values as shown in Figure 5 and VCC = 5.0 V. In the expandor mode, the typical input dynamic range was from -34 dB to +12 dB where 0 dB is equal to 100 mVRMS. The typical unity gain level measured at 0 dB @ 1.0 kHz input was "0.5 dB and the typical tracking error was "0.1 dB for input range of -30 to +10 dB. In the compressor mode, the typical input dynamic range was from -42 dB to "18 dB with a tracking error +0.1 dB and the typical unity gain level was "0.5 dB. In the ALC mode, the typical input dynamic range was from -42 dB to +8.0 dB with typical output deviation of "0.2 dB about the nominal output of 0 dB. For input greater than +9.0 dB in ALC configuration, the summing amplifier sometimes exhibits high frequency oscillations. There are several solutions to this problem. The first is to lower the values of R6 and R7 to 20 k W each. The second is to add a current limiting resistor in series with C12 at Pin 13. The third is to add a compensating capacitor of about 22 to 30 pF between the input and output of summing amplifier (Pins 12 and 14). With any one of the above recommendations, the typical ALC mode input range increased to +18 dB yielding a dynamic range of over 60 dB. |
Similar Part No. - SA575N |
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Similar Description - SA575N |
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