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ML1490PP Datasheet(PDF) 7 Page - LANSDALE Semiconductor Inc. |
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ML1490PP Datasheet(HTML) 7 Page - LANSDALE Semiconductor Inc. |
7 / 8 page www.lansdale.com Page 7 of 8 Issue A LANSDALE Semiconductor, Inc. ML1490 DESCRIPTION OF SPEECH COMPRESSOR The amplifier drives the base of a PNP transistor operating common–emitter with a voltage gain of approximately 20. The control R1 varies the quiescent Q point of this transistor so that varying amounts of signal exceed the level Vr. Diode D1 rectifies the positive peaks of Q1's output only when these peaks are greater than Vr ≈ 7.0 V. The resulting output is fil- tered by Cx, Rx. Rx controls the charging time constant or attack time. Cx is involved in both charge and discharge. R2 (the 150 k Ω and input resistance of the emitter–follower Q2) controls the decay time. Making the decay long and attack short is accomplished by making Rx small and R2 large. (A Darlington emitter–fol- lower may be needed if extremely slow decay times are required.) The emitter–follower Q2 drives the AGC Pin 5 of the ML1490PP and reduces the gain. R3 controls the slope of sig- nal compression. Table 1. Distortion versus Frequency Frequency Distortion Distortion Frequency 10 mV ei 100 mV ei 10 mV ei 100 mV ei 100 Hz 3.5% 12% 15% 27% 300 Hz 2% 10% 6% 20% 1.0 kHz 1.5% 8% 3% 9% 10 kHz 1.5% 8% 1% 3% 100 kHz 1.5% 8% 1% 3% Notes 1 and 2 Notes 3 and 4 Notes: (1) Decay = 300 ms (3) Decay = 20 ms Attack = 20 ms Attack = 3.0 ms (2) Cx = 7.5 µF (4) Cx = 0.68 µF Rx = 0 (Short) Rx = 1.5 kΩ 5 Figure 24. Speech Compressor ML1490 25 µF 0.001 1.0 k 1.0 k +12 V 2 4 6 1 3 8 10 µF 10 µF Output +12 V +12 V 2.2 k 220 15 µF Input 15 µF R3 15 k Q2 2N3904 +12 V 7 Q1 2N3906 4.7 k 150 k R2 Cx Rx D1 6.8 k R1 100 k 33 k Vr |
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