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345 results found, displaying items 341 - 345
Detector yields sensitivity with ultra-low power consumption
RF ID tags, circuits that detect a “wake-up” call and return a burst of data, must operate on a very low quiescent current for weeks or months, yet have enough battery power in reserve to answer an incoming call. If the system operates in the...
Precision DC motor speed controller
Optical tachometers that produce a frequency proportional to RPM are popular feedback sources for precision analog motor speed control. This usually involves a frequency-to-voltage converter (FVC) to convert the tachometer output to a voltage that’s...
Dual-output voltage regulator converts 5V to 12V and 3.3V
Today’s microprocessors need a regulated 3.3-V supply that can provide several amperes of current. To obtain this, a synchronous switching regulator (LTC1266-3.3) using a 5-V supply is usually used with a p-channel top-side MOSFET and an n-channel...
Missing pulse detector protects transformer
Designed as part of the controller of an astronomical telescope, this circuit delivers an ac drive waveform to the drive motor. The frequency of the ac output is set by an external oscillator that generates the desired drive rate. But what...
Build IF/AGC Amp With Four Parts
An IF/AGC amplifier that features an 82-dB AGC range can be built using just four active components (see the figure). It uses a simple two-transistor peak detector (the transistors, 2N3904 and 2N3906, are commonly available and low cost). The peak detector consists of Q2, a temperature-dependent current source, and Q1, a half-wave detector. Q2 is biased for a collector current of 300 µA at 27°C; the temperature...
RMS Converter Has Excellent CMR
Designs for rms converters are common, particularly the single-chip monolithic solutions. This circuit (see the figure), however, differs from the others because of its versatile instrumentation-amplifier-type differential inputs that feature excellent common-mode rejection (CMR). In addition, the circuit is built with inexpensive, generic components. The first step in input-signal processing is the differential-input absolute-value...
Filter Improves Stop-Band Rejection
Most op amps have a low output impedance at frequencies well below their closed-loop bandwidth, but as frequency increases, so does the output impedance. When the op amp is used in a Sallen-Key low-pass filter, this increase in output impedance can reduce the filter's stopband rejection. However, a simple emitter-follower buffer amplifier at the op amp's output can reduce the effects of the higher output impedance and improve the stop-band rejection. The...
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