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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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MCP41010E/P датащи(PDF) 15 Page - Microchip Technology |
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MCP41010E/P датащи(HTML) 15 Page - Microchip Technology |
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15 / 32 page  2003 Microchip Technology Inc. DS11195C-page 15 MCP41XXX/42XXX 4.2 Typical Applications 4.2.1 PROGRAMMABLE SINGLE-ENDED AMPLIFIERS Potentiometers are often used to adjust system refer- ence levels or gain. Programmable gain circuits using digital potentiometers can be realized in a number of different ways. An example of a single-supply, inverting gain amplifier is shown in Figure 4-4. Due to the high input impedance of the amplifier, the wiper resistance is not included in the transfer function. For a single-sup- ply, non-inverting gain configuration, the circuit in Figure 4-5 can be used. . FIGURE 4-4: Single-supply, programmable, inverting gain amplifier using a digital potentiometer. FIGURE 4-5: Single-supply, programmable, non-inverting gain amplifier. In order for these circuits to work properly, care must be taken in a few areas. For linear operation, the analog input and output signals must be in the range of VSS to VDD for the potentiometer and input and output rails of the op-amp. The circuit in Figure 4-4 requires a virtual ground or reference input to the non-inverting input of the amplifier. Refer to Application Note 682, “Using Single-Supply Operational Amplifiers in Embedded Systems” (DS00682), for more details. At power-up or reset (RS), the resistance is set to mid-scale, with RA and RB matching. Based on the transfer function for the circuit, the gain is -1 V/V. As the code is increased and the wiper moves towards the A terminal, the gain increases. Conversely, when the wiper is moved towards the B terminal, the gain decreases. Figure 4-6 shows this relationship. Notice the pseudo-logarithmic gain around decimal code 128. As the wiper approaches either terminal, the step size in the gain calculation increases dramatically. Due to the mismatched ratio of RA and RB at the extreme high and low codes, small increments in wiper position can dramatically affect the gain. As shown in Figure 4-3, recommended gains lie between 0.1 and 10 V/V. FIGURE 4-6: Gain vs. Code for inverting and differential amplifier circuits. 4.2.2 PROGRAMMABLE DIFFERENTIAL AMPLIFIER An example of a differential input amplifier using digital potentiometers is shown in Figure 4-7. For the transfer function to hold, both pots must be programmed to the same code. The resistor-matching from channel-to- channel within a dual device can be used as an advan- tage in this circuit. This circuit will also show stable operation over temperature due to the low potentiome- ter temperature coefficient. Figure 4-6 also shows the relationship between gain and code for this circuit. As the wiper approaches either terminal, the step size in the gain calculation increases dramatically. This circuit is recommended for gains between 0.1 and 10 V/V. MCP606 VIN VSS -IN +IN VOUT B A W MCP41010 Where: VREF + - VDD VOUT VIN RB RA ------- V REF 1 RB RA ------- + + – = RA RAB 256 Dn – () 256 --------------------------------------- = RB RABDn 256 ------------------ = RAB Total Resistance of pot = Dn Wiper setting forDn 0 to 255 = = MCP606 VIN VSS VDD +IN -IN VOUT RB RA W MCP41010 + - Where: RA RAB 256 Dn – () 256 --------------------------------------- = RB RABDn 256 ------------------ = RAB Total Resistance of pot = Dn Wiper setting forDn 0 to 255 = = VOUT VIN 1 RB RA ------- + = 0.1 1 10 0 64 128 192 256 Decimal code (0-255) |
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