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MCP6001 bảng dữ liệu(PDF) 9 Page - Microchip Technology |
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MCP6001 bảng dữ liệu(HTML) 9 Page - Microchip Technology |
9 / 24 page 2003 Microchip Technology Inc. DS21733D-page 9 MCP6001/2/4 3.6.3 PEAK DETECTOR The MCP6001/2/4 op amp has a high input impedance, rail-to-rail input and output and low input bias current, which makes this device suitable for a peak detector applications. Figure 3-7 shows a peak detector circuit with clear and sample switches. The peak-detection cycle uses a clock (CLK), as shown in Figure 3-7. At the rising edge of CLK, Sample Switch closes to begin sampling. The peak voltage stored on C1 is sam- pled to C2 for a sample time defined by tSAMP. At the end of the sample time (falling edge of Sample Signal), Clear Signal goes high and closes the Clear Switch. When the Clear Switch closes, C1 discharges through R1 for a time defined by tCLEAR. At the end of the clear time (falling edge of Clear Signal), op amp A begins to store the peak value of VIN on C1 for a time defined by tDETECT. In order to define the tSAMP and tCLEAR, it is necessary to determine the capacitor charging and discharging period. The capacitor charging time is limited by the amplifier source current, while the discharging time ( τ) is defined using R1 ( τ = R1*C1). tDETECT is the time that the input signal is sampled on C1, and is dependent on the input voltage change frequency. The op amp output current limit, and the size of the storage capacitors (both C1 and C2), could create slew- ing limitations as the input voltage (VIN) increases. Cur- rent through a capacitor is dependent on the size of the capacitor and the rate of voltage change. From this relationship, the rate of voltage change or the slew rate can be determined. For example, with op amp short-cir- cuit current of ISC = 25 mA and load capacitor of C1 = 0.1 µF, then: EQUATION This voltage change rate is less than the MCP6001/2/4 slew rate of 600 mV/µs. When the input voltage swings below the voltage across C1, D1 becomes reverse- biased, which opens the feedback loop and rails the amplifier. When the input voltage increases, the ampli- fier recovers at its slew rate. Based on the rate of volt- age change shown in the above equation, it takes an extended period of time to charge a 0.1 µF capacitor. The capacitors need to be selected so that the circuit is not limited by the amplifier slew rate. Therefore, the capacitors should be less than 40 µF and a stabilizing resistor (RISO) needs to be properly selected. Refer to Section 3.3, “Capacitive Load and Stability”, for op amp stability. FIGURE 3-7: Peak Detector with Clear and Sample CMOS Analog Switches. dVC1 dt ------------- ISC C1 -------- = 25mA 0.1 µF --------------- = dVC1 dt ------------- 250mV µs ----------------- = ISC C1 dVC1 dt ------------- × = VIN MCP6002 VC1 MCP6002 D1 A B VOUT MCP6001 C C2 Sample Signal Clear Signal Clear RISO Sample – + – + – + CLK tSAMP tCLEAR tDETECT Switch Switch 1/2 1/2 R1 RISO VC2 C1 |
Số phần tương tự - MCP6001 |
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Mô tả tương tự - MCP6001 |
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