Hi, This question is about digital PLL design. The DPLL is in fact a software PLL according to some PLL's definition. It calculates the phase error with hardware. This phase error passes through a typical digital PI filter, arrives at a NCO. I want to design a similar PLL. Before implementation, I would like to simulate this PLL in Matlab. The questions are about the phase detector unit and NCO unit. The phase detector gain Kd is shown as: 1 unit/rad The NCO gain is 20 MHz/unit. This DPLL is in fixed point number. What does 1 unit mean in above two lines? Is it the whole digital range, or the least bit (LSB)? Or it is something else? Here are the original data: Parameter Value Lock-in Range ΔωL 7.5 KHz Damping Factor ξ 0.707 Natural Frequency ωn 3.3 x 10^4 rad/s Phase Detector Gain Kd 1 unit/rad NCO Gain Ko 20 MHz/unit PI Filter Coefficient C1 2^-11 PI Filter Coefficient C2 2^-14 Thanks for help me.
What does unit/rad mean in DPLL phase detector?
Started by ●March 22, 2014
Reply by ●March 23, 20142014-03-23
On Sat, 22 Mar 2014 19:59:54 -0700, fl wrote:> Hi, > > This question is about digital PLL design. The DPLL is in fact a > software PLL according to some PLL's definition. It calculates the phase > error with hardware. This phase error passes through a typical digital > PI filter, arrives at a NCO. I want to design a similar PLL. Before > implementation, I would like to simulate this PLL in Matlab. The > questions are about the phase detector unit and NCO unit. > > The phase detector gain Kd is shown as: 1 unit/rad > > The NCO gain is 20 MHz/unit. > > > This DPLL is in fixed point number. What does 1 unit mean in above two > lines? Is it the whole digital range, or the least bit (LSB)? Or it is > something else?It's whatever the original designer wanted it to be. If the fixed point scheme has a fractional part (i.e., if it's anything but integers), then I would guess that 1 unit is 1. If not, and particularly if the designer was not a native English speaker, your guess is as good as mine. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●March 23, 20142014-03-23
On Sun, 23 Mar 2014 00:50:38 -0500, Tim Wescott <tim@seemywebsite.really> wrote:>On Sat, 22 Mar 2014 19:59:54 -0700, fl wrote: > >> Hi, >> >> This question is about digital PLL design. The DPLL is in fact a >> software PLL according to some PLL's definition. It calculates the phase >> error with hardware. This phase error passes through a typical digital >> PI filter, arrives at a NCO. I want to design a similar PLL. Before >> implementation, I would like to simulate this PLL in Matlab. The >> questions are about the phase detector unit and NCO unit. >> >> The phase detector gain Kd is shown as: 1 unit/rad >> >> The NCO gain is 20 MHz/unit. >> >> >> This DPLL is in fixed point number. What does 1 unit mean in above two >> lines? Is it the whole digital range, or the least bit (LSB)? Or it is >> something else? > >It's whatever the original designer wanted it to be. If the fixed point >scheme has a fractional part (i.e., if it's anything but integers), then >I would guess that 1 unit is 1. If not, and particularly if the designer >was not a native English speaker, your guess is as good as mine. > >-- > >Tim Wescott >Wescott Design Services >http://www.wescottdesign.comWhat Tim said. I like to us an MSB as a unit for a fixed-point implementation, although one can get creative and use many other things. The main thing is to be consistent across the analysis. This may help: http://www.compdsp.com/presentations/Jacobsen/abineau_dpll_analysis.pdf Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
Reply by ●March 23, 20142014-03-23
On Sun, 23 Mar 2014 17:58:45 +0000, Eric Jacobsen wrote:> On Sun, 23 Mar 2014 00:50:38 -0500, Tim Wescott > <tim@seemywebsite.really> wrote: > >>On Sat, 22 Mar 2014 19:59:54 -0700, fl wrote: >> >>> Hi, >>> >>> This question is about digital PLL design. The DPLL is in fact a >>> software PLL according to some PLL's definition. It calculates the >>> phase error with hardware. This phase error passes through a typical >>> digital PI filter, arrives at a NCO. I want to design a similar PLL. >>> Before implementation, I would like to simulate this PLL in Matlab. >>> The questions are about the phase detector unit and NCO unit. >>> >>> The phase detector gain Kd is shown as: 1 unit/rad >>> >>> The NCO gain is 20 MHz/unit. >>> >>> >>> This DPLL is in fixed point number. What does 1 unit mean in above two >>> lines? Is it the whole digital range, or the least bit (LSB)? Or it is >>> something else? >> >>It's whatever the original designer wanted it to be. If the fixed point >>scheme has a fractional part (i.e., if it's anything but integers), then >>I would guess that 1 unit is 1. If not, and particularly if the >>designer was not a native English speaker, your guess is as good as >>mine. >> >>-- >> >>Tim Wescott Wescott Design Services http://www.wescottdesign.com > > What Tim said. I like to us an MSB as a unit for a fixed-point > implementation, although one can get creative and use many other things. > The main thing is to be consistent across the analysis. > > This may help: > > http://www.compdsp.com/presentations/Jacobsen/abineau_dpll_analysis.pdfIt helps that the phase detector is in unit/radian and the NCO is in Hz/ unit -- that means that whatever a "unit" may be, the phase detector gain times NCO gain is known to be 20MHz/radian. That, in turn, means that as long as the controller is behaving linearly, the system behavior depends only on the controller transfer function. Of course, it's a PLL, and with those the devil is in the (nonlinear) details. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
