| Electronics > Projects, Designs, and Technical Stuff |
| 1.5 to 3 MHz frequency doubler circuit |
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| edavid:
--- Quote from: Benta on January 02, 2019, 04:04:10 pm ---Problem is, that the simple XOR phase/frequency detector does not have phase coherence. It can be anywhere between -90 and +90 degrees. --- End quote --- That is not correct. A PLL with filtered XOR phase detector will always lock at 90 degrees phase difference. :-// |
| Benta:
--- Quote from: edavid on January 02, 2019, 04:23:18 pm --- --- Quote from: Benta on January 02, 2019, 04:04:10 pm ---Problem is, that the simple XOR phase/frequency detector does not have phase coherence. It can be anywhere between -90 and +90 degrees. --- End quote --- That is not correct. A PLL with filtered XOR phase detector will always lock at 90 degrees phase difference. --- End quote --- Your understanding is incorrect. A type 1 PLL (which an XOR PD is) has varying phase difference between the input signals, depending on which voltage the VCO needs. Otherwise it would not work as FM detector, for instance. I recommend that you invest in a Gardner ~100$). |
| nick_d:
Check specs on TAS5755M master clock, it is highly unlikely it would need a 50% duty cycle unless it's sampling the data on both clock edges. At around 10MHz with HC logic the 50% duty cycle becomes inportant to avoid pulses that are too narrow for the logic to handle, but this is unlikely to be a problem at 3MHz and at 3.3V you will be using more advanced logic anyway. So how I would handle this is the Schmitt XOR... you only need 1 gate, just put the undelayed 1.5MHz in one input and the RC delayed 1.5MHz in the other. The Schmitt wouldn't be needed with HC logic at MHz rates since by the time it had switched the input would be well past threshold preventing oscillation, but it might be beneficial with more advanced logic. If you are usng 1 gate packages get the Schmitt XOR. Otherwise if you have spare gates let us know and we may be able to see a way. cheers, Nick |
| Gandalf_Sr:
I ordered some parts from Digikey today so that I can try some of the approaches suggested here. Quantity Part Number Manufacturer Part Number Description 10 296-17660-1-ND SN74AUP1G79DCKR IC FF D-TYPE SNGL 1BIT 2 296-14856-1-ND SN74HC590ADWR IC 8BIT BINARY COUNTR 3ST 10 296-27397-1-ND SN74AUP1T86DCKR IC GATE XOR SCHMITT 1CH 10 296-21048-1-ND SN74LV4046ADGVR IC LOGIC PLL W/VCO 10 712-1274-1-ND 500R07S220GV4T CAP CER 22PF 50V C0G/NP0 10 TC33X-103ECT-ND TC33X-2-103E TRIMMER 10K OHM 0.1W J LEAD Not much money and they will all come in for experimentation - the Caps are 2% vs the 20% ones that I used before |
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