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BA3423S датащи(PDF) 10 Page - Rohm |
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BA3423S датащи(HTML) 10 Page - Rohm |
10 / 18 page 260 Audio ICs BA3423S FCircuit operation (1) Playback equalizer amplifier The standard input level is *76dBm at 315Hz. The volt- age gain at 315Hz is 53dB, so the standard output level for the playback equalizer amplifier is *23dBm. The playback head is connected between the bias pin (pin 28) and the input pins without coupling capacitors, and the amplifier input stage is biased through the head. When the A / B switch pin (pin 20) is “H”, the input goes to B, and when it is open the input goes to A. The play- back equalizer NAB characteristics are determined as follows: External CR timing circuit: 270k Ω, 4.7kΩ, 0.012µF On-chip resistors: 5.3k Ω, 500Ω Bass time constant: = 270k Ω 0.012 µF 3180 µs Treble time constant: Normal-speed mode: = (4.7k Ω + 5.3kΩ) 0.012 µF = 120µs High-speed mode: = (4.7k Ω + 500Ω) 0.012 µF = 62.4µs Switching between normal-speed and high-speed modes is controlled by pin 21 (Nor / HS). When pin 21 is HIGH, high-speed mode is selected, and when open, normal-speed mode is selected. (2) Aux input amplifier The standard input level is *23dBm, and the input resis- tance is 47k Ω. Input the CD or radio signal (or other) via a coupling ca- pacitor. Switch the Tape / Aux input (pin 18) “H” for Aux in- put mode, and leave it open for tape input mode. (3) Microphone amplifier The standard microphone input level is *50dBm when the NF resistor connected to the Mic NF pin (pin 22) is 820 Ω. The microphone amplifier gain at this time is 27dB, and the microphone amplifier output is *23dB. The input resistance of the Mic In pin (pin 23) is 30k Ω. Connect the input to pin 23 via a coupling capacitor. The frequency characteristics of the microphone amplifier are deter- mined by the bass cutoff frequency of the CR circuit con- nected to the Mic NF pin. For treble cutoff, connect a low- pass filter circuit to the input pin. (4) Function switching (Mic / mixing circuit) The signal switched by the Tape / Aux switching pin (pin 18) and the microphone amplifier output are mixed by a 6.8k Ω mixing resistor. However, when the Nor/HS pin is set to high-speed mode (“H”), the microphone amplifier output is muted. When in internal microphone recording mode (only when: pin 18 is open (tape mode), pin 19 is “H” (recording mode), pin 20 is “H” (Tape B mode), and pin 21 is open (normal-speed mode)), the tape and Aux inputs are muted, and only the Mic output is output. If pin 21 is driven “H” (high-speed mode) in this state, all inputs are muted. Pins 16 and 17 are for the low-pass filter. These pins cut bias oscillation leakage during dubbing. The 6.8k Ω mixing resistor and an external capacitor set the treble cutoff frequency according to the following for- mula fHC = 1 / ( πCR) Treble cutoff frequency: fHC (Hz) Mixing resistor: R = 6.8k ( Ω) External capacitor: C (F) (5) Line amplifier The standard level of the signal mixed by the mixing re- sistor is *30dBm. This level is input as is to the line am- plifier. The gain of the line amplifier is 11dB, so the stan- dard output is *19dBm, and this is output to the Line Out pins (pins 14 and 15). The line amplifier output has a mute switch, but it is only muted when in internal micro- phone recording mode (described in the previous item). The line mute operates to suppress the switching “pop” sound that is generated when switching between modes (transient muting). The transient muting time is set by the time constants of the external circuits connected the con- trol pins (pins 18 to 21). However, in one case only, when pin 18 is “H” (Aux input mode), line output muting does not occur when the other control pins are switched. This is to disable transient line out muting when recording is started while listening to the radio (for example). |
Аналогичный номер детали - BA3423S |
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Аналогичное описание - BA3423S |
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