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AD603AR-REEL7 Datenblatt(PDF) 9 Page - Analog Devices |
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AD603AR-REEL7 Datenblatt(HTML) 9 Page - Analog Devices |
9 / 14 page AD603 REV. C –9– VC 3.0 –0.1 2.5 2.0 1.5 1.0 0.5 0.0 –0.5 –1.0 –1.5 –2.0 –2.5 –3.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Figure 13. Gain Error for Cascaded Stages–Low Ripple Mode VC –0.2 90 85 80 75 70 65 60 55 50 0 0.2 0.4 0.6 0.8 1.0 1.2 Figure 14. ISNR vs. Control Voltage–Low Ripple Mode THEORY OF THE AD603 A Low Noise AGC Amplifier Figure 15 shows the ease with which the AD603 can be connected as an AGC amplifier. The circuit illustrates many of the points previously discussed: It uses few parts, has linear-in-dB gain, operates from a single supply, uses two cascaded amplifiers in sequential gain mode for maximum S/N ratio, and an external resistor programs each amplifier’s gain. It also uses a simple temperature-compensated detector. The circuit operates from a single 10 V supply. Resistors R1, R2, R3, and R4 bias the common pins of A1 and A2 at 5 V. This pin is a low impedance point and must have a low impedance path to ground, here provided by the 100 µF tantalum capacitors and the 0.1 µF ceramic capacitors. The cascaded amplifiers operate in sequential gain. Here, the offset voltage between the pins 2 (GNEG) of A1 and A2 is 1.05 V (42.14 dB × 25 mV/dB), provided by a voltage divider consisting of resistors R5, R6, and R7. Using standard values, the offset is not exact, but it is not critical for this application. The gain of both A1 and A2 is programmed by resistors R13 and R14, respectively, to be about 42 dB; thus the maximum gain of the circuit is twice that, or 84 dB. The gain-control range can be shifted up by as much as 20 dB by appropriate choices of R13 and R14. The circuit operates as follows. A1 and A2 are cascaded. Capacitor C1 and the 100 Ω of resistance at the input of A1 form a time-constant of 10 µs. C2 blocks the small dc offset voltage at the output of A1 (which might otherwise saturate A2 at its maximum gain) and introduces a high-pass corner at about 16 kHz, eliminating low frequency noise. A half-wave detector is used, based on Q1 and R8. The current into capacitor CAV is just the difference between the collector current of Q2 (biased to be 300 µA at 300 K, 27°C) and the col- lector current of Q1, which increases with the amplitude of the A2 AD603 10V C8 0.1 F C2 0.1 F R14 2.49k 10V + R4 2.49k C6 0.1 F C5 100 F2 R3 2.49k A1 AD603 10V C7 0.1 F C1 0.1 F R13 2.49k 10V + R2 2.49k C4 0.1 F C3 100 F2 R1 2.49k RT 100 1 J1 R7 3.48k R6 1.05k R5 5.49k 1V OFFSET FOR SEQUENTIAL GAIN 5.5V 6.5V NOTES 1R T PROVIDES A 50 INPUT IMPEDANCE 2C3 AND C5 ARE TANTALUM 10V AGC LINE CAV 0.1 F THIS CAPACITOR SETS AGC TIME CONSTANT VAGC R9 1.54k R8 806 Q1 2N3904 Q2 2N3906 R10 1.24k R11 3.83k 5V R12 4.99k C11 0.1 F C9 0.1 F 10V J2 C10 0.1 F Figure 15. A Low Noise AGC Amplifier |
Ähnliche Teilenummer - AD603AR-REEL7 |
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Ähnliche Beschreibung - AD603AR-REEL7 |
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