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LMC1982CIN データシート(PDF) 9 Page - National Semiconductor (TI) |
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LMC1982CIN データシート(HTML) 9 Page - National Semiconductor (TI) |
9 / 14 page Application Information (Continued) if the total emitter current exceeds 5 mA. Thus, maximum output voltage can be increased and much lower distortion levels can be achieved using load impedances of at least 25 k Ω. INPUT IMPEDANCE The input impedance of pins 4, 5, 24 and 25 is defined by in- ternal bias resistors and is typically 50 k Ω. The SELECT IN pins have an input impedance that varies with the BASE and TREBLE control settings. The input im- pedance is 100 k Ω at DC and 19 kΩ at 1 kHz when the con- trols are set at 0 dB. Minimum input impedance of 30.4 k Ω at DC and 16 k Ω at 1 kHz occurs when maximum boost is se- lected. At 10 kHz the minimum input impedance, with the tone controls flat, is 6.8 k Ω and, with the tone controls at maximum boost, is 2.5 k Ω. EXTERNAL SIGNAL PROCESSING The SELECT OUT pins (6 and 23) enable greater system design flexibility by providing a means to implement an ex- ternal processing loop. This loop can be used for noise re- duction circuits such as DNR (LM1894) or multi-band graphic equalizers (LMC835). If both are used, it is important to ensure that the noise reduction circuitry precede the equalization circuits. Failure to do so results in improper op- eration of the noise reduction circuits. The system shown in Figure 3 utilizes the external loop to include DNR and a multi-band equalizer. TONE CONTROL RESPONSE Bass and treble tone controls are included in the LMC1982. The tone controls used just two external capacitors for each stereo channel. Each has a corner frequency determined by the value of C2 and C3 (see Figure 4) and internal resistors in the feedback loop of the internal tone amplifier. The maximum-boost or cut is determined by the data sent to the LMC1982 (see Table 1). The typical tone control response shown in Typical Perfor- mance Curves were generated with C2 = C3 = 0.0082 µF and show the response for each step. When modifying the tone control response it is important to note that the ratio of C3 and C2 sets the mid-frequency gain. Symmetrical tone response is achieved when C2 = C3. However, with C2 = 2(C3) and the tone controls set to “flat”, the frequency response will be flat at 20 Hz and 20 kHz, and +6 dB at 1 kHz. The frequency where a tone control begins to deviate from a flat response is referred to as the turn-over frequency. With C = C2 = C3, the LMC1982’s treble turn-over frequency is nominally DS011028-6 FIGURE 2. Input and Mode Select Circuitry www.national.com 9 |
同様の部品番号 - LMC1982CIN |
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同様の説明 - LMC1982CIN |
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