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LMV105M5 データシート(PDF) 8 Page - National Semiconductor (TI) |
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LMV105M5 データシート(HTML) 8 Page - National Semiconductor (TI) |
8 / 12 page Application Information (Continued) 3.0 Capacitive Load Tolerance The LMV101/102/105/110 can directly drive 200pF capaci- tive load with Vs = 5V at −1 gain configuration without oscil- lation. Direct capacitive loading reduces the phase margin of amplifiers. The combination of the amplifier’s output imped- ance and the capacitive load induces phase lag. This results in either an underdamped pulse or oscillation. To drive a heavier capacitive load, a resistive isolation can be used as shown in Figure 1. The isolation resistor R iso and the CL form a pole to increase stability by adding more phase margin to the overall system. The desired performance depends on the value of R iso. The bigger the R iso resistor value, the more stable VOUT will be. Figure 2 is an output waveform of Figure 1 using 100 Ω for R iso and 1000pF for CL. 4.0 Phase Inverting AC Amplifier A single supply phase inverting AC amplifier can be easily built with the LMV101/102/105/110 series ( Figure 3). The output voltage is biased at mid-supply, and AC input signal is amplified by (R 2/R1). Capacitor CIN acts as an input AC cou- pling capacitor to block DC potentials. A capacitor of 0.1µF or larger can be used. The output can swing rail-to-rail. To avoid output distortion, the peak-to-peak amplitude of the input AC signal should be less than V CC(R 1/R2). It is recommended that a small-valued capacitor be used across the feedback resistor (R 2) to eliminate stability prob- lems, prevent peaking of the response, and limit the band- width of the circuit. This can also help to reduce high fre- quency noise and some other interference. (See Figure 4) 5.0 Microphone preamplifier Most microphones have a low output voltage level. This out- put signal needs to be amplified so that it can feed the next stage with optimal level. Figure 5 shows a microphone preamplifier circuit with the LMV110. This microphone preamplifier can provide 20dB gain. It can be implemented in PCs, PDAs, and mobile phones. Input capacitor C IN serves two important functions. First, it blocks any DC voltage from the previous stage to prevent the output from shifting to some unwanted DC level. This could cause the output to saturate when audio signal is ap- plied at the input. Second, the C IN and the 10k input resistor form a low pass filter to block any low frequency noise. The cut-off frequency of this low pass filter is given by, where R 1 = 10kΩ in LMV110. Output capacitor COUT is used to block the DC output from the next stage. R bias is selected according to the microphone requirement. DS101234-13 FIGURE 1. Resistive Isolation of a Heavy Capacitive Load DS101234-12 FIGURE 2. Pulse Response of LMV101 in Figure 1 DS101234-10 FIGURE 3. Phase Inverting AC Amplifier DS101234-11 FIGURE 4. www.national.com 8 |
同様の部品番号 - LMV105M5 |
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同様の説明 - LMV105M5 |
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