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Shielding and Guarding: AN-347 - Analog Devices Application Notes (added 2/06) How to Exclude Interference-Type
Noise. What to do and Why to do it-A Rational Approach
Switched capacitor IC
controls feedback loop: 02/17/00 EDN -Design Ideas / (Schematic / circuit design added 08/05) You can implement a simple control loop with a constant setpoint over a wide
range of control by using a switched-capacitor filter. The circuit controls motor speed over 1 to 200 Hz or 60 to 12,000 rpm. In Figure 1, a National LMF40CIWM four-pole lowpass filter is the
heart of the design. This filter has a cutoff frequency defined by the clock divided by 50. Consider this filter as a difference amplifier that compares the difference between two frequencies.
The relationship between the clock divided by 50 and the 500-count encoder divided by 2 is such that when the clock rate is 1000 times the revolutions per second of the motor, the signal
frequency from the encoder is at approximately the midpoint of the filter response. This midpoint is the point of zero error and is approximately 2V p-p. The rectified output serves as the dc
setpoint voltage for the control loop. If the motor speed increases, the voltage decreases, and if the motor slows down, the voltage increases. As simple as the method is, it can drive a
motor-control chip and provide good speed regulation....
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