Hi, I apologise if this is not strictly DSP related, but it is still signal processing related. Basically my question is how one can get a 90 degree phase shifted version of a sinusoidal wave using analog components. The only challenge is that the frequency will not be fixed. For a fixed frequency, one could use an all-pass filter. (Are there any other solutions for a fixed frequency.) Basically, I am trying to build a QPSK modulator, and would like to implement frequency hopping as well. Is there a way that this could be done digitally at say 433 MHz? Any thoughts, suggestions and/or pointers to literature would be greatly appreciated. Jaco Versfeld
Slightly O.T.: 90 degree phase shift of sinusoidal wave using analog components
Started by ●November 21, 2006
Reply by ●November 21, 20062006-11-21
jaco.versfeld@gmail.com wrote:> Hi, > > I apologise if this is not strictly DSP related, but it is still signal > processing related. > > Basically my question is how one can get a 90 degree phase shifted > version of a sinusoidal wave using analog components. The only > challenge is that the frequency will not be fixed.The legalistic answer is "no", but it can be done well enough. There are circuits that accept an audio input and produce a pair of outputs that are nearly 90 degrees apart from one another. Such circuits become very difficult to trim if the bandwidth much exceeds a decade or if quadrature must be maintained to better than a few tenth of a degree. The phase response of either output relative to the input is well defined, but not very interesting. The one I built used six op-amps.> For a fixed frequency, one could use an all-pass filter. (Are there > any other solutions for a fixed frequency.) > > Basically, I am trying to build a QPSK modulator, and would like to > implement frequency hopping as well. > > Is there a way that this could be done digitally at say 433 MHz? > > Any thoughts, suggestions and/or pointers to literature would be > greatly appreciated.What signal do you need to shift? The RF oscillator can have a pair of quadrature outputs at all frequencies. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●November 21, 20062006-11-21
jaco.versfeld@gmail.com wrote:> Basically my question is how one can get a 90 degree phase shifted > version of a sinusoidal wave using analog components. The only > challenge is that the frequency will not be fixed.This is indeed possible. However it all depends on how accurate should be the phase shift over the bandwidth of interest.> > For a fixed frequency, one could use an all-pass filter. (Are there > any other solutions for a fixed frequency.)There are many possible solutions depending on the application. Perhaps, the simplest is to make a Chebyshev approximation of the desired phase shift using a bunch of allpass filters.> > Basically, I am trying to build a QPSK modulator, and would like to > implement frequency hopping as well.I see. Basically, you want to suppress the unwanted sideband.> > Is there a way that this could be done digitally at say 433 MHz?It is possible, however why would you need to do it at 433 MHz? Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●November 21, 20062006-11-21
Jerry Avins wrote:>> Basically my question is how one can get a 90 degree phase shifted >> version of a sinusoidal wave using analog components. The only >> challenge is that the frequency will not be fixed. > > > The legalistic answer is "no", but it can be done well enough. There are > circuits that accept an audio input and produce a pair of outputs that > are nearly 90 degrees apart from one another. Such circuits become very > difficult to trim if the bandwidth much exceeds a decade or if > quadrature must be maintained to better than a few tenth of a degree. > The phase response of either output relative to the input is well > defined, but not very interesting. The one I built used six op-amps. >Tuning of the direct analog phase shifter is very tricky, and I doubt if the accuracy of better then 1% is achievable, especially including all of the drifts. However there were hideous solutions of the quadrature shifters with making the SSB signal using filters and then converting it back to baseband. Probably, 0.1% is as good as it can be done. VLV
Reply by ●November 21, 20062006-11-21
Vladimir Vassilevsky wrote:> > > Jerry Avins wrote: > > >>> Basically my question is how one can get a 90 degree phase shifted >>> version of a sinusoidal wave using analog components. The only >>> challenge is that the frequency will not be fixed. >> >> >> The legalistic answer is "no", but it can be done well enough. There >> are circuits that accept an audio input and produce a pair of outputs >> that are nearly 90 degrees apart from one another. Such circuits >> become very difficult to trim if the bandwidth much exceeds a decade >> or if quadrature must be maintained to better than a few tenth of a >> degree. The phase response of either output relative to the input is >> well defined, but not very interesting. The one I built used six op-amps. >> > > Tuning of the direct analog phase shifter is very tricky, and I doubt if > the accuracy of better then 1% is achievable, especially including all > of the drifts. However there were hideous solutions of the quadrature > shifters with making the SSB signal using filters and then converting it > back to baseband. Probably, 0.1% is as good as it can be done.My method of tuning involved no interaction between trimmers. The signal passed through two chains of three all-passes each, emerging from them in near quadrature. The precise frequency of quadrature for each of the all-pass sections is not difficult to calculate with the help of a computer. I set them with an accurately settable signal generator (Krohn-Hite digital) and a synchronous detector (MiniCircuits diode bridge) driven by the stage's input and nulling its detected output. The shifter achieved 1.125 decades (300 to 4000 Hz) and 1/4 degree at 20 C. Other measures would have been needed for an extended temperature range. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●November 21, 20062006-11-21
<jaco.versfeld@gmail.com> wrote in message news:1164095780.785134.255820@j44g2000cwa.googlegroups.com...> Hi, > > I apologise if this is not strictly DSP related, but it is still signal > processing related. > > Basically my question is how one can get a 90 degree phase shifted > version of a sinusoidal wave using analog components. The only > challenge is that the frequency will not be fixed. > > For a fixed frequency, one could use an all-pass filter. (Are there > any other solutions for a fixed frequency.) > > Basically, I am trying to build a QPSK modulator, and would like to > implement frequency hopping as well. > > Is there a way that this could be done digitally at say 433 MHz? > > Any thoughts, suggestions and/or pointers to literature would be > greatly appreciated. > Jaco Versfeld >If it's a pure sine wave then use a phase-locked loop. when in lock the VCO output will be in phase quadrature with the inpute AND tract frequency variations. Only trouble is it will normally be a square wave output. M. -- Posted via a free Usenet account from http://www.teranews.com
Reply by ●November 22, 20062006-11-22
"Major Misunderstanding" <mad@uni.com> writes:> <jaco.versfeld@gmail.com> wrote in message > news:1164095780.785134.255820@j44g2000cwa.googlegroups.com... >> Hi, >> >> I apologise if this is not strictly DSP related, but it is still signal >> processing related. >> >> Basically my question is how one can get a 90 degree phase shifted >> version of a sinusoidal wave using analog components. The only >> challenge is that the frequency will not be fixed. >> >> For a fixed frequency, one could use an all-pass filter. (Are there >> any other solutions for a fixed frequency.) >> >> Basically, I am trying to build a QPSK modulator, and would like to >> implement frequency hopping as well. >> >> Is there a way that this could be done digitally at say 433 MHz? >> >> Any thoughts, suggestions and/or pointers to literature would be >> greatly appreciated. >> Jaco Versfeld >> > > If it's a pure sine wave then use a phase-locked loop. when in lock > the VCO output will be in phase quadrature with the inputeUnless you do something special to the phase detector, it wouldn't be in quadrature but in direct lock. Now if you could somehow introduce a 90-degree offset in the phase detector, you'd be talking. -- % Randy Yates % "How's life on earth? %% Fuquay-Varina, NC % ... What is it worth?" %%% 919-577-9882 % 'Mission (A World Record)', %%%% <yates@ieee.org> % *A New World Record*, ELO http://home.earthlink.net/~yatescr
Reply by ●November 22, 20062006-11-22
Randy Yates wrote: ...> Unless you do something special to the phase detector, it wouldn't be > in quadrature but in direct lock. > > Now if you could somehow introduce a 90-degree offset in the phase > detector, you'd be talking.The simplest analog PLLs use an XOR gate as a phase detector. The local oscillator is locked to quadrature by such circuits. Digital PLLs can be built the same way, but they aren't necessarily simplest. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●November 22, 20062006-11-22
Jerry Avins <jya@ieee.org> writes:> Randy Yates wrote: > > ... > >> Unless you do something special to the phase detector, it wouldn't be >> in quadrature but in direct lock. >> Now if you could somehow introduce a 90-degree offset in the phase >> detector, you'd be talking. > > The simplest analog PLLs use an XOR gate as a phase detector. The > local oscillator is locked to quadrature by such circuits. Digital > PLLs can be built the same way, but they aren't necessarily simplest.What if the designer didn't want quadrature lock but direct lock? -- % Randy Yates % "She has an IQ of 1001, she has a jumpsuit %% Fuquay-Varina, NC % on, and she's also a telephone." %%% 919-577-9882 % %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr
Reply by ●November 22, 20062006-11-22
Jaco, Why not just use something like the TRF 3701? http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=632&uiTemplateId=NODE_STRY_PGE_T¶mCriteria=no -- % Randy Yates % "She's sweet on Wagner-I think she'd die for Beethoven. %% Fuquay-Varina, NC % She love the way Puccini lays down a tune, and %%% 919-577-9882 % Verdi's always creepin' from her room." %%%% <yates@ieee.org> % "Rockaria", *A New World Record*, ELO http://home.earthlink.net/~yatescr
