If you do not allow these cookies, you will experience reduced relevant content. As you know, a sine wave (without any additional phase) is shifted by 90° relative to a cosine wave. They do not store directly personal information, but are based on uniquely identifying your browser and internet device. They may be used by Analog Devices to build a profile of your interests and show you relevant content on our site. Targeting Cookies: These cookies may be set through our site by Analog Devices and our service providers. Quadrature phase shift keying (QPSK) is another modulation technique, and its a particularly interesting one because it actually transmits two bits per symbol. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance. All information these cookies collect is aggregated and therefore anonymous. They help us to know which pages are the most and least popular and see how visitors move around the site. Performance Cookies: These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. If you do not allow these cookies then some or all of these services may not function properly. They may be set by us or by third party providers whose services we have added to our pages. Functional Cookies: These cookies enable the website to provide enhanced functionality and personalization. These cookies do not store any personally identifiable information. You can set your browser to block or alert you about these cookies, but some parts of the site will not then work. They are usually only set in response to actions made by you which amount to a request for services, such as setting your privacy preferences, logging in or filling in forms. Strictly Necessary Cookies: (Always Active) These cookies are necessary for the website to function and cannot be switched off in our systems. are dened as the power-split difference and phase difference, respectively, between. After we finish updating our website, you will be able to set your cookie preferences. (quadrature) phase relationship between the through and coupled paths. Oh well looks like I’ll have to dive in myself and try to work it out.Analog Devices is in the process of updating our website. He does explain what he did in a presentation, referenced in this thread, but it’s involved…. Both have a frequency of 2MHz with a DC offset proportional to the phase shift, confirming the above mathematics. Figures 2 and 3 show the 'in-phase' waveform, V I, and the 'quadrature' waveform, V Q, respectively. Don’t believe he’s keen to provide his code. The input voltage, QPSK IN, is a 1MHz sine wave whose phase is shifted by 45, 135, 225, and then 315 every 5s. Looking at the Si5351 documentation, this is an involved process, that doesn’t appear to be covered in the standard libraries available for the si5351a, though it has been solved by Hans Summers of QRP labs. If this kind of techniques are further extended, PSK can be done by eight or sixteen values also, depending upon the requirement. Usually 2 d flip flops are driven at a frequency 4 times higher than the required clock to generate the required, but I believe this isn’t perfect, and better results can be achieved by running 2 clocks from the si5351a and phase adjusting 1 with respect to the other. Quadrature Phase Shift Keying (QPSK) This is the phase shift keying technique, in which the sine wave carrier takes four phase reversals such as 0°, 90°, 180°, and 270°. All I know is maintaining accurate phase shift between the clocks is all important as inaccuracies will effect the quality of the demodulated signal and unwanted side band suppression. I’m driving a multiplexer that samples an rf signal to generate I and Q signals for demodulation of an ssb signal by phase shift either with op amps or with audio dsp in a microcontroller. My requirements are for a quadrature clocks with as little as possible gitter between each as is possible with the Si5351a. You are right I can’t define phase noise mathematically. This seems a bit "iffy", but it apparently works well: (Google translate link) To get frequencies lower than 3 MHz with the 5351 one technique is to set up two outputs with frequencies perhaps 1/10th or 1/100th Hz difference, wait the correct amount of time (that allows the two clocks to shift into quadrature), then change the divider so the frequencies are equal. Here's a link to a good presentation of this technique: See page 14. Yes, the lower frequency limit for this setup is around 3 MHz, and if I recall correctly the upper limit is VCO/8, or around 112 MHz. To get fine control of the frequency you then adjust the PLL frequency. With the proper output divider and phase control (delay) divider values you can get an extremely accurate quadrature output. The Si5351 phase control resolution has limited resolution, but is quite precise.
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