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| + | ====== Clock Shapers ====== | ||
| + | ==== Capacitor coupled Clock Shaper ==== | ||
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| + | The circuit shown below has a wide bandwidth [<10KHz, > 100MHz]. Input amplitude range is [100mV - 5V]pp. | ||
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| + | {{:clockshaper3.gif|}} | ||
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| + | Originally designed for use in a linear phase detector there are other applications for which it is suitable. | ||
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| + | The design is derived from the input clock shaping circuit in the HP K34-5991A. A comparator with a CMOS/TTL compatible output is substituted for the ECL differential amplifiers in the K34-5991A. For higher frequencies either an ECL or LVDS comparator can be used. | ||
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| + | ==== Transformer coupled Clock Shaper ==== | ||
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| + | The circuit shown below works over the 0.1MHz to 100MHz frequency range and is intended to produce a TTL/CMOS compatible output when the input amplitude is known and well controlled. As shown the circuit is intended for operation with a +7dB input signal. For lower frequencies other comparators like the AD8561 can be used. For higher frequencies an ECL or LVDS comparator can be used with a suitable transformer. | ||
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| + | {{:timing_clockshaperii.gif|}} | ||
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| + | ==== Filtering sinewave clock sources to minimise harmonic and subharmonic content. ==== | ||
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| + | Although a high Q narrow bandpass filter is the obvious approach, using such a filter will severely degrade the phase shift tempco. Its better from the perspective of phase shift stability to use a low pass filter with low phase shift at the signal frequency supplemented by high Q bandstop filters tuned to the frequencies of the harmonics or subharmonics to be eliminated. Such filters can have low phase shift and associated tempco at the signal frequency. | ||
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| + | Bruce Griffiths | ||