Quadrature low pass filter question
in [DSP]
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From: Zhi.Shen on 12 May 2010 00:39 "Jerry Avins" <jya(a)ieee.org> ??????:GIfGn.1275$gv4.1122(a)newsfe09.iad... > On 5/11/2010 5:21 AM, Zhi.Shen wrote: >> If you just don't want to implement the LPF twice, you can double your >> LPF >> system clock to complete the I and Q's LP process in only one filter. > > Oh? How do you deal with perpetual start-up "transients"? > I'm not very sure what the "transients" are. In my opinion, for example, if the I,Q interpolation need 10-tap filtering at sampling rate 10MHz each, I can use two 100MHz 'Serial' LPFs or just one time division multiplex 200MHz 'Serial' LPF to complete it.
From: glen herrmannsfeldt on 12 May 2010 00:47 John O'Flaherty <quiasmox(a)yeeha.com> wrote: (snip, I wrote) >>Otherwise, it reminds me of stories from the early days of >>CD players, using one ADC for both stereo channels, alternating >>between the two. The resulting half sample period delay was >>said to be audible by some people. > That would correspond to a stereo speaker positioning error of 0.15 > inches. Maybe they were hearing something else. Maybe they have clamps to keep their head in the right position. I suppose with headphones you might be able to do it. -- glen
From: Randy Yates on 12 May 2010 06:22 Jerry Avins <jya(a)ieee.org> writes: > [...] > As long as we both know what we mean and have the same operations in > mind, straightening out the semantics os secondary to me. I didn't think this was simply a matter of semantics. I know a company that was getting 130 MHz bandwidth in the late 80's - no mean feat even for today - by utilizing complex sampling (of course that meant they had to convert to quadrature in analog). My main point is that there are practical, as well as theoretical, differences between the two techniques and they are not "the same thing." Now before you tell me how you can build a "2x"-Hz A/D from x-Hz A/D components, let me say that this is an exercise in A/D converter design and not directly relevent to the discussion. For once you've got a "2x"-Hz A/D designed, you can then get 2x-Hz bandwidth through it by utilizing two such converters on a complex I/Q signal. -- Randy Yates % "And all you had to say Digital Signal Labs % was that you were mailto://yates(a)ieee.org % gonna stay." http://www.digitalsignallabs.com % Getting To The Point', *Balance of Power*, ELO
From: Jerry Avins on 12 May 2010 09:59 On 5/12/2010 12:39 AM, Zhi.Shen wrote: > "Jerry Avins"<jya(a)ieee.org> ??????:GIfGn.1275$gv4.1122(a)newsfe09.iad... >> On 5/11/2010 5:21 AM, Zhi.Shen wrote: >>> If you just don't want to implement the LPF twice, you can double your >>> LPF >>> system clock to complete the I and Q's LP process in only one filter. >> >> Oh? How do you deal with perpetual start-up "transients"? >> > > I'm not very sure what the "transients" are. > In my opinion, for example, if the I,Q interpolation need 10-tap filtering > at sampling rate 10MHz each, I can use two 100MHz 'Serial' LPFs or just one > time division multiplex 200MHz 'Serial' LPF to complete it. A filter has history. In the case of an FIR with taps, is is the contents of the circular buffer. Each output is computed from all of the buffer stages. If you alternate inputs between channels, the outputs will be garbage. There are ways to combine resources, but beyond reusing the tap coefficients, they save very little memory. Jerry -- "I view the progress of science as ... the slow erosion of the tendency to dichotomize." --Barbara Smuts, U. Mich. �����������������������������������������������������������������������
From: Jerry Avins on 12 May 2010 10:24
On 5/12/2010 6:22 AM, Randy Yates wrote: > Jerry Avins<jya(a)ieee.org> writes: >> [...] >> As long as we both know what we mean and have the same operations in >> mind, straightening out the semantics os secondary to me. > > I didn't think this was simply a matter of semantics. I know a company > that was getting 130 MHz bandwidth in the late 80's - no mean feat even > for today - by utilizing complex sampling (of course that meant they had > to convert to quadrature in analog). > > My main point is that there are practical, as well as theoretical, > differences between the two techniques and they are not "the same > thing." > > Now before you tell me how you can build a "2x"-Hz A/D from x-Hz A/D > components, let me say that this is an exercise in A/D converter design > and not directly relevent to the discussion. For once you've got a > "2x"-Hz A/D designed, you can then get 2x-Hz bandwidth through it by > utilizing two such converters on a complex I/Q signal. Same thing or different, one can get (nearly) X bandwidth with 2X samples/sec. Those samples can be sequential, I&Q, X&dX/dt, and other possible pairs. Do we agree on that? Jerry -- "I view the progress of science as ... the slow erosion of the tendency to dichotomize." --Barbara Smuts, U. Mich. ����������������������������������������������������������������������� |