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Demodulator Circuits
Last Updated on:
Saturday, June 27, 2009 04:42 PM |
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Links to electronic circuits,
electronic schematics, designs for engineers, hobbyists, students & inventors:
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Ber Meter is Easy to Build: 03/02/00 EDN-Design Ideas / (added 1/06) A
bit-error-rate (BER) tester is a basictool for digital-communications measurements.
Although many commercial BER testers are available, you can easily design and build an
inexpensive version. The scheme in Figure 1 has performance similar to that of a
commercial tester but requires you to perform a manual calculation based on displayed
data. The tester displays received bits and received erroneous bits, and you must
calculate the BER data using a handheld calculator, for example.... |
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Circuit Yields Accurate Absolute Values: 07/05/01 EDN-Design Ideas / (added
1/05 The circuit in Figure 1 delivers the absolute value of the input signal with an
accuracy better than 10 ppm of the full-scale range. The circuit has low zero-crossing
error. You can use it as an asynchronous demodulator, as a source for logarithmic
amplifiers, or simply as a demonstration of the wonders of feedback. The circuit uses
two op amps; five identical resistors, R; one double-value resistor, 2R; and four
thermally matched diodes. When the input, VIN, is positive, IC1's output is 2VIN+VD3
(the voltage drop across D3). D2 is reverse-biased, thus IC2 behaves as a voltage
follower, yielding VOUT=R(VIC1-VD4)/2R. Because the same amount of current (VIN/R)
flows in D3 and D4, assuming their characteristics are the same, VD3=VD4, and
VOUT=VIN. When VIN is negative, IC1's output is 2VIN-VD1. D4 is reverse-biased, and
IC2 is an inverting amplifier, yielding VOUT=R(VIC1+VD2)/2R. Again, the current
flowing in D1 and D2 is VIN/R, and VOUT=-VIN. For good performance,... |
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Clock Recovery Scheme Suits Low Snr Systems: 06/05/00 EDN-Design Ideas /
(Electronic circuit added 7/03) A clock-recovery architecture can operate with NRZ
digital signals, even at low SNRs. A clock-recovery subsystem is based on a PLL
comprising a phase comparator, a loop filter, and a voltage-controlled oscillator
(VCO).... |
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Demodulator Schematic/Design: The demodulator block diagram below has three
major sections that were implemented in this iteration of the design, the mixer, the
filter, and the phase shift network (Electronic circuit added 7/03) |
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Inverted Bipolar Transistor Doubles as a Signal Clamp: 06/07/01EDN-Design
Ideas / (Electronic circuit added 7/03) A number of circuits, such as level detectors
and AM demodulators, benefit from a rectifier with a low offset voltage. Silicon
diodes have an offset of approximately 0.6V and do not work well in low-level
circuitry. A Schottky diode is a bit better... |
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Inverted Bipolar Transistor Doubles as a Signal Clamp: 11/09/00 EDN-Design
Ideas / (Electronic circuit added 7/03) A number of circuits, such as level detectors
and AM demodulators, benefit from a rectifier with a low offset voltage.... |
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Novel Method Detects Lock in Costas Loops: 06/22/00 EDN-Design Ideas /
(Electronic circuit added 7/03) In the well-established lock-detection scheme for
conventional PLLs, the VCO or VCXO local oscillator splits the output into 0 and
90 signals ( Figure 1 ). The incoming IF signal mixes with the 0 and 90 signals to
perform phase locking and lock detection,... |
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Self Modifying Code Extends Addressing Mode: 12/17/98 EDN-Design Ideas
/ (added 07/05) As just about any assembly-language programmer knows,
self-modifying code (SMC) is usually undesirable, unintentional, and destructive.
However, the SMC routine in Listing 1 is extremely useful to extend the indexed,
16-bit offset addressing mode of the venerable HC05 µC from 8 bits, or 256
locations, to the full 13-bit (8-kbyte) memory address space that the µC’s
architecture supports. This routine is very useful for error tables, text messages
tables, or any array manipulation for a large number of elements.... |
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Simple Ber Meter is Easy to Build: 03/02/00 EDN-Design Ideas / (added
1/06) A bit-error-rate (BER) tester is a basictool for digital-communications
measurements. Although many commercial BER testers are available, you can easily
design and build an inexpensive version. The scheme in Figure 1 has performance
similar to that of a commercial tester but requires you to perform a manual
calculation based on displayed data. The tester displays received bits and
received erroneous bits, and you must calculate the BER data using a handheld
calculator, for example.... |
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Single Sideband Demodulator Covers the Hf Band #1: 07/20/00 EDN-Design
Ideas / (Electronic circuit added 7/03) The circuit in Figure 1 complements a
previous Design Idea ( Reference 1 ). The modulator used a phasing network to
split a low-frequency (audio) signal into in-phase and quadrature (orthogonal)
components. The phasing network has an advantage over... |
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Single Sideband Demodulator Covers the Hf Band #2: 10/26/00 EDN-Design
Ideas / (Electronic circuit added 7/03) The circuit in Figure 1 complements a
previous Design Idea (" SSB modulator covers HF band ," EDN , Sept 30, 1999, pg
122). The modulator employs a phasing network to split a low-frequency audio
signal into in-phase and quadrature (orthogonal) compo... |
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Spread Spectrum Method Identifies Audio Path: 04/13/00 EDN-Design Ideas
/ (added 8/04) An unusual method of audio spread spectrum can identify the audio
path that's currently in use through a consumer-electronic device. The design in
Figure 1a uses an injected audio spread-spectrum tag signal because a listener
does not notice the low... |
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