Can I somehow obtain IQ Data by using two ADCs on same input real signal and are there some limitations to this? I see Texas Instrument ADCs have two channels named I and Q but I do not understand if I have two inputs (for two analog signals representing I and Q) or they form I and Q from real signal. Thank you very much in advance. --------------------------------------- Posted through http://www.DSPRelated.com
IQ Data from ADC
Started by ●September 29, 2015
Reply by ●September 29, 20152015-09-29
On Tue, 29 Sep 2015 09:47:06 -0500, b2508 wrote:> Can I somehow obtain IQ Data by using two ADCs on same input real signal > and are there some limitations to this? > > I see Texas Instrument ADCs have two channels named I and Q but I do not > understand if I have two inputs (for two analog signals representing I > and Q) or they form I and Q from real signal. > > Thank you very much in advance.Does this help? http://dspguru.com/dsp/tricks/complex-downconverters-at-fs-over-4 Allan
Reply by ●September 29, 20152015-09-29
>Can I somehow obtain IQ Data by using two ADCs on same input real signal >and are there some limitations to this? > >I see Texas Instrument ADCs have two channels named I and Q but I do not >understand if I have two inputs (for two analog signals representing Iand>Q) or they form I and Q from real signal. > >Thank you very much in advance. >--------------------------------------- >Posted through http://www.DSPRelated.comDoesn't seem necessary to use the ADC to do this if its ultimately ending up in a processor where you can take your real input signal and decompose it. This basically boils down to turning your real signal into an analytic signal see this post for details: http://www.dsprelated.com/freebooks/mdft/Analytic_Signals_Hilbert_Transform.html --------------------------------------- Posted through http://www.DSPRelated.com
Reply by ●September 29, 20152015-09-29
On 9/29/2015 10:47 AM, b2508 wrote:> Can I somehow obtain IQ Data by using two ADCs on same input real signal > and are there some limitations to this? > > I see Texas Instrument ADCs have two channels named I and Q but I do not > understand if I have two inputs (for two analog signals representing I and > Q) or they form I and Q from real signal. > > Thank you very much in advance.The ADC is two ADCs in one package... or it's possible they are combining two ADCs with an analog mixer which can turn one analog signal into two. Or another possibility is a single ADC with a digital mixer following which creates I and Q. You didn't share a part number with us. I am not familiar with TI's full product line. -- Rick
Reply by ●September 29, 20152015-09-29
On Tue, 29 Sep 2015 09:47:06 -0500, b2508 wrote:> Can I somehow obtain IQ Data by using two ADCs on same input real signal > and are there some limitations to this? > > I see Texas Instrument ADCs have two channels named I and Q but I do not > understand if I have two inputs (for two analog signals representing I > and Q) or they form I and Q from real signal.Post specific data sheets. One can obtain inphase and quadrature data by taking your one real signal, phase shifting it into two signals 90 degrees apart, and then converting. This has it's downsides -- it's sensitive to the different gains in the channels as well as to phase shifts that aren't exactly 90 degrees. Sampling with a single fast ADC and doing the quadrature conversion in digital-land saves you from that, but it does so at the cost of needing a faster ADC and at least some fast logic to do the conversion. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●September 30, 20152015-09-30
>On 9/29/2015 10:47 AM, b2508 wrote: >> Can I somehow obtain IQ Data by using two ADCs on same input realsignal>> and are there some limitations to this? >> >> I see Texas Instrument ADCs have two channels named I and Q but I donot>> understand if I have two inputs (for two analog signals representing I >and >> Q) or they form I and Q from real signal. >> >> Thank you very much in advance. > >The ADC is two ADCs in one package... or it's possible they are >combining two ADCs with an analog mixer which can turn one analog signal>into two. Or another possibility is a single ADC with a digital mixer >following which creates I and Q. You didn't share a part number with >us. I am not familiar with TI's full product line. > >-- > >Rick--------------------------------------- Posted through http://www.DSPRelated.com
Reply by ●September 30, 20152015-09-30
I am using ADC12D800RF. I don't understand if I can, by using one single analog input obtain iq data with this ADC. This ADC basically has 2 channels named I and Q but from what I've understood, it can use both of them to sample the same input signal with, say, fs and obtain 2*fs rate that way. But is this IQ data and if it is, how is that the case? --------------------------------------- Posted through http://www.DSPRelated.com
Reply by ●September 30, 20152015-09-30
>On Tue, 29 Sep 2015 09:47:06 -0500, b2508 wrote: > >> Can I somehow obtain IQ Data by using two ADCs on same input realsignal>> and are there some limitations to this? >> >> I see Texas Instrument ADCs have two channels named I and Q but I donot>> understand if I have two inputs (for two analog signals representing I >> and Q) or they form I and Q from real signal. >> >> Thank you very much in advance. > > >Does this help? >http://dspguru.com/dsp/tricks/complex-downconverters-at-fs-over-4 > >AllanI am not sure if this is what I need. I receive IF data on one analog channel (real data) and then this goes through ADC. I get real data at the output and this goes to DDC and I get IQ Data. My question is, can I get IQ data from ADC and then instead of feeding real data to DDC, feed IQ data to it? I am not sure what is the benefit of this and what is the reason but it is a requirement. --------------------------------------- Posted through http://www.DSPRelated.com
Reply by ●September 30, 20152015-09-30
On 9/30/2015 3:15 AM, b2508 wrote:> I am using ADC12D800RF. I don't understand if I can, by using one single > analog input obtain iq data with this ADC. > This ADC basically has 2 channels named I and Q but from what I've > understood, it can use both of them to sample the same input signal with, > say, fs and obtain 2*fs rate that way. But is this IQ data and if it is, > how is that the case?No, this will not be I/Q data. If you sample a data stream you can then multiply the real stream with a complex quadrature signal which will give you I/Q samples. What do you wish to do with this data once it is I/Q data? -- Rick
Reply by ●September 30, 20152015-09-30
On 9/30/2015 3:30 AM, b2508 wrote:>> On Tue, 29 Sep 2015 09:47:06 -0500, b2508 wrote: >> >>> Can I somehow obtain IQ Data by using two ADCs on same input real > signal >>> and are there some limitations to this? >>> >>> I see Texas Instrument ADCs have two channels named I and Q but I do > not >>> understand if I have two inputs (for two analog signals representing I >>> and Q) or they form I and Q from real signal. >>> >>> Thank you very much in advance. >> >> >> Does this help? >> http://dspguru.com/dsp/tricks/complex-downconverters-at-fs-over-4 >> >> Allan > > I am not sure if this is what I need. > > I receive IF data on one analog channel (real data) and then this goes > through ADC. I get real data at the output and this goes to DDC and I get > IQ Data. > My question is, can I get IQ data from ADC and then instead of feeding > real data to DDC, feed IQ data to it? > > I am not sure what is the benefit of this and what is the reason but it is > a requirement.Such a strange requirement. The DDC is generating I/Q data by digitally multiplying (mixing) your real data stream with a complex carrier (quadrature). You can do the same mixing in the analog domain and sample the two I/Q analog signals with the ADC chip you have chosen. Is that what you are looking for? Seems a lot easier to do in the digital domain using your DDC chip. Why do you need to feed the DDC chip I/Q data? -- Rick