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LA3161-E датащи(PDF) 4 Page - ON Semiconductor |
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LA3161-E датащи(HTML) 4 Page - ON Semiconductor |
4 / 7 page LA3161 www.onsemi.com 4 Function of External Parts C2, C4 are input coupling capacitors. In NAB equalizer amplifier, the gain at low frequencies is high and 1/f noise inside the IC is emphasized as output noise. Therefore, if the reactance of capacitor at low frequencies is increased, the dependence of 1/f noise on the signal source resistance causes the output noise voltage to deteriorate, and the value of reactance must be made small enough as compared with the signal source resistance. C2, C4 also influence the operation start time and the adequate value of these capacitors is 10 F. (Since C2, C4 of less than 4.7F make the operation start time longer, use C2, C4, of 4.7F or more). C5, C11 are NF capacitors. The lower cut-off frequency depends on the value of these capacitors. If the lower cut-off frequency is taken as fL : C5 (C11) = 1/2 · fL · R2 (R7) If the value of this capacitor is made larger, the operation start time of amplifier is more delayed. The adequate value of capacitor is 47 F. The frequency characteristic of the equalizer amplifier depends on C6 and R4, R3 (C10 and R5, R6). The time constants to obtain the standard NAB characteristic are as shown below. Tape speed 9.5cm/s 4.75cm/s C6 (R3 R4) 3180 s 1590 s R3 C6 90 s 120 s C8 is bias capacitor for the power line. C8 of 47F is inserted at a point as close to the power supply pin (pin 4) as possible. C1, C3 are for preventing radio interference in the strong electric field, interference attributable to engine noise, and blocking oscillation at the time of large amplitude operation. The adequate value of C1, C3 is approximately 1000pF. C7, C9 are output coupling capacitors. The adequate value of C7, C9 is 10F. NAB element and determination of gain Since the DC feedback is provided by R1, R2 of NAB element, which brings about DC output potential at pins 3, 6, it is impossible to change the value of R1, R2 of NAB element greatly. Therefore, when determining the gain, change RNF with R1, R2, C1 (NAB element) kept constant. (1) How to obtain RNF Impedance Z of NAB element is Z = 1 1/R1 + j C1 + R2 = (R1 + R2) 1 + j C1{R1 R2/(R1 + R2)} 1 + j C1R1 For a general negative feedback amplifier circuit, A = Ao/ (1 + Ao ) applies, and Z = A · RNF is obtained under conditions of Ao>>A, A>>1 ( = RNF/ (RNF + Z), Ao = open-loop gain, A = feedback gain). Therefore, we can use an approximation of RNF = Z/A. A = (VG for 1kHz) times, (Set R1, R2 at approximately 100k) Each time constant of NAB characteristic. Tape speed 9.5cm/s 4.75cm/s T1 C1, R1 3180 s 1590 s T2 C1 (R1//R2) 90 s 120 s (2) Examples of NAB Constants (a) Tape speed : 9.5cm/s. (8 tracks) VG : RNF (VG/f = 1kHz) VG 30 35 40 dB RNF 180 100 56 |
Аналогичный номер детали - LA3161-E |
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Аналогичное описание - LA3161-E |
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