Digital bandwidth

Hi

I am currently working on a project which involves determining the
relationship between the the "bandwidth"(as my advisor puts it)  and
power consumption of an I/Q transmitter. The I/Q transmitter works as
follows:

In-Phase: Even bits of PN sequence ---> DAC ---> LPF --> multiply by
cosine --> transmit

Quad-Phase: Odd bits of PN sequence --> DAC --> LPF --> mult. by sine
--> transmit

The problem is that my advisor wants me to see how the power
consumption changes as you change the bandwidth of the input data (the
PN sequence). I have a power model and a power estimator worked out
nicely for the transmitter itself. However, I dont know what he means
by changing the bandwidth of the input data. Does it mean that I change
the pattern of 1s and 0s or just increase/decrease the number of bits
(resolution) of the PN sequence? Please help, I have come this far
working hard on my simulator and I dont want to stop short just on
something small I don't understand for the simulation itself.

Thank You
Mohammed Billoo

billoo wrote:
> Hi
> 
> I am currently working on a project which involves determining the
> relationship between the the "bandwidth"(as my advisor puts it)  and
> power consumption of an I/Q transmitter. The I/Q transmitter works as
> follows:
> 
> In-Phase: Even bits of PN sequence ---> DAC ---> LPF --> multiply by
> cosine --> transmit
> 
> Quad-Phase: Odd bits of PN sequence --> DAC --> LPF --> mult. by sine
> --> transmit
> 
> The problem is that my advisor wants me to see how the power
> consumption changes as you change the bandwidth of the input data (the
> PN sequence). I have a power model and a power estimator worked out
> nicely for the transmitter itself. However, I dont know what he means
> by changing the bandwidth of the input data. Does it mean that I change
> the pattern of 1s and 0s or just increase/decrease the number of bits
> (resolution) of the PN sequence? Please help, I have come this far
> working hard on my simulator and I dont want to stop short just on
> something small I don't understand for the simulation itself.

I don't understand what you need. some people seem to feel that my 
asking questions is an attack, but my only other course is ignoring you.

1) Is there a reason you can't ask your adviser?

2) A DAC operation is usually performed on several bits at a time. If 
you are sending ones and zeros, what does the DAC operation consist of?

3) How is the PN sequence production related to the LPF bandwidth?

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

Jerry Avins wrote:
> billoo wrote:
> > Hi
> >
> > I am currently working on a project which involves determining the
> > relationship between the the "bandwidth"(as my advisor puts it)  and
> > power consumption of an I/Q transmitter. The I/Q transmitter works as
> > follows:
> >
> > In-Phase: Even bits of PN sequence ---> DAC ---> LPF --> multiply by
> > cosine --> transmit
> >
> > Quad-Phase: Odd bits of PN sequence --> DAC --> LPF --> mult. by sine
> > --> transmit
> >
> > The problem is that my advisor wants me to see how the power
> > consumption changes as you change the bandwidth of the input data (the
> > PN sequence). I have a power model and a power estimator worked out
> > nicely for the transmitter itself. However, I dont know what he means
> > by changing the bandwidth of the input data. Does it mean that I change
> > the pattern of 1s and 0s or just increase/decrease the number of bits
> > (resolution) of the PN sequence? Please help, I have come this far
> > working hard on my simulator and I dont want to stop short just on
> > something small I don't understand for the simulation itself.
>
> I don't understand what you need. some people seem to feel that my
> asking questions is an attack, but my only other course is ignoring you.
>
> 1) Is there a reason you can't ask your adviser?
>
> 2) A DAC operation is usually performed on several bits at a time. If
> you are sending ones and zeros, what does the DAC operation consist of?
>
> 3) How is the PN sequence production related to the LPF bandwidth?
>
> Jerry
> --
> Engineering is the art of making what you want from things you can get.
> =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=
=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=
=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF

1) I have asked my pofessor and he is working on numerous projects and
it takes him a while to reply to my emails and I saw that the groups
generally respond quickly.

2) My project involves modelling the power consumption of the ZigBee
CC2420 radio module.  I modelled the DAC as an R-2R ladder which means
that a 1 closes a circuit for a set of resistors to generate a
particular output voltage and the 0 leaves the circuit open.

3) I am not concerned about the analag bandwidth but the digital
bandwidth of the data stream going into the DAC. I want to graph the
change in digital bandwidth from 0 to pi versus the power consumed by
the analog component (since it is the most power hungry). So basically,
I have the data stream of 1s and 0s coming out of the digital part of
the circuit. I want to vary the bandwidth of the 1s and 0s and then see
how the power consumed of the analog circuit changes. My question is
what does the bandwidth of digital signal depend on (e.g. number of 1s
and 0s, bit resolution)?=20

Thank You
Mohammed Billoo

Mohammed, Jerry's questions are often more instructive than some 
answers. Some pupils of DSP object to being required to think. Students 
do it and then realize why mentor asked the question. If you are not a 
native English speaker [ or even if you are ] a study of the fine 
distinctions between "pupil" and "student" would be instructive.

Jerry, ask away. The ignorant will be made wise and foolish will be 
offended.

Editorial comment.
  *TOO many* "student bodies" are just a conglomeration of pupils.

PS. I think Mohammed can be used as an example of "How to Ask a Question".



billoo wrote:
> Jerry Avins wrote:
> 
>>billoo wrote:
>>
>>>Hi
>>>
>>>I am currently working on a project which involves determining the
>>>relationship between the the "bandwidth"(as my advisor puts it)  and
>>>power consumption of an I/Q transmitter. The I/Q transmitter works as
>>>follows:
>>>
>>>In-Phase: Even bits of PN sequence ---> DAC ---> LPF --> multiply by
>>>cosine --> transmit
>>>
>>>Quad-Phase: Odd bits of PN sequence --> DAC --> LPF --> mult. by sine
>>>--> transmit
>>>
>>>The problem is that my advisor wants me to see how the power
>>>consumption changes as you change the bandwidth of the input data (the
>>>PN sequence). I have a power model and a power estimator worked out
>>>nicely for the transmitter itself. However, I dont know what he means
>>>by changing the bandwidth of the input data. Does it mean that I change
>>>the pattern of 1s and 0s or just increase/decrease the number of bits
>>>(resolution) of the PN sequence? Please help, I have come this far
>>>working hard on my simulator and I dont want to stop short just on
>>>something small I don't understand for the simulation itself.
>>
>>I don't understand what you need. some people seem to feel that my
>>asking questions is an attack, but my only other course is ignoring you.
>>
>>1) Is there a reason you can't ask your adviser?
>>
>>2) A DAC operation is usually performed on several bits at a time. If
>>you are sending ones and zeros, what does the DAC operation consist of?
>>
>>3) How is the PN sequence production related to the LPF bandwidth?
>>
>>Jerry
>>--
>>Engineering is the art of making what you want from things you can get.
>>�����������������������������������������������������������������������
> 
> 
> 1) I have asked my pofessor and he is working on numerous projects and
> it takes him a while to reply to my emails and I saw that the groups
> generally respond quickly.
> 
> 2) My project involves modelling the power consumption of the ZigBee
> CC2420 radio module.  I modelled the DAC as an R-2R ladder which means
> that a 1 closes a circuit for a set of resistors to generate a
> particular output voltage and the 0 leaves the circuit open.
> 
> 3) I am not concerned about the analag bandwidth but the digital
> bandwidth of the data stream going into the DAC. I want to graph the
> change in digital bandwidth from 0 to pi versus the power consumed by
> the analog component (since it is the most power hungry). So basically,
> I have the data stream of 1s and 0s coming out of the digital part of
> the circuit. I want to vary the bandwidth of the 1s and 0s and then see
> how the power consumed of the analog circuit changes. My question is
> what does the bandwidth of digital signal depend on (e.g. number of 1s
> and 0s, bit resolution)? 
> 
> Thank You
> Mohammed Billoo
> 

billoo wrote:
> Jerry Avins wrote:
>> billoo wrote:
>>> Hi
>>>
>>> I am currently working on a project which involves determining the
>>> relationship between the the "bandwidth"(as my advisor puts it)  and
>>> power consumption of an I/Q transmitter. The I/Q transmitter works as
>>> follows:
>>>
>>> In-Phase: Even bits of PN sequence ---> DAC ---> LPF --> multiply by
>>> cosine --> transmit
>>>
>>> Quad-Phase: Odd bits of PN sequence --> DAC --> LPF --> mult. by sine
>>> --> transmit
>>>
>>> The problem is that my advisor wants me to see how the power
>>> consumption changes as you change the bandwidth of the input data (the
>>> PN sequence). I have a power model and a power estimator worked out
>>> nicely for the transmitter itself. However, I dont know what he means
>>> by changing the bandwidth of the input data. Does it mean that I change
>>> the pattern of 1s and 0s or just increase/decrease the number of bits
>>> (resolution) of the PN sequence? Please help, I have come this far
>>> working hard on my simulator and I dont want to stop short just on
>>> something small I don't understand for the simulation itself.
>> I don't understand what you need. some people seem to feel that my
>> asking questions is an attack, but my only other course is ignoring you.
>>
>> 1) Is there a reason you can't ask your adviser?
>>
>> 2) A DAC operation is usually performed on several bits at a time. If
>> you are sending ones and zeros, what does the DAC operation consist of?
>>
>> 3) How is the PN sequence production related to the LPF bandwidth?
>>
>> Jerry
>> --
>> Engineering is the art of making what you want from things you can get.
>> �����������������������������������������������������������������������
> 
> 1) I have asked my pofessor and he is working on numerous projects and
> it takes him a while to reply to my emails and I saw that the groups
> generally respond quickly.
> 
> 2) My project involves modelling the power consumption of the ZigBee
> CC2420 radio module.  I modelled the DAC as an R-2R ladder which means
> that a 1 closes a circuit for a set of resistors to generate a
> particular output voltage and the 0 leaves the circuit open.

Unless there is something decidedly peculiar about the transmitter 
module, it's power consumption is independent of the modulating waveform 
if it is FM or PM, and proportional to the duty cycle if it is AM. The 
duty cycle is not a function of bandwidth.

PN sequences make good streams of random bits, but groups of N 
successive bits make poor random numbers, I suggest that you get your 
pseudo-random numbers some other way, say with a well designed linear 
congruential generator.

> 3) I am not concerned about the analag bandwidth but the digital
> bandwidth of the data stream going into the DAC. I want to graph the
> change in digital bandwidth from 0 to pi versus the power consumed by
> the analog component (since it is the most power hungry). So basically,
> I have the data stream of 1s and 0s coming out of the digital part of
> the circuit. I want to vary the bandwidth of the 1s and 0s and then see
> how the power consumed of the analog circuit changes. My question is
> what does the bandwidth of digital signal depend on (e.g. number of 1s
> and 0s, bit resolution)? 

The bandwidth of a stream of random numbers is 1/2 the number-generation 
rate. Higher frequencies that you might imagine are present are aliased 
into that range or removed by the reconstruction filter that follows the 
DAC. (That's what the LPF is for. Properly designed, it passes no 
significant amount of any frequency higher than half the sample rate.)

4) Are you sure you understood what your professor asked you to do?

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

Richard Owlett wrote:

   ...

> PS. I think Mohammed can be used as an example of "How to Ask a Question".

I agree.

Far too many posts here are examples of "How *Not* to Ask a Question".

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

billoo wrote:
>My question is
> what does the bandwidth of digital signal depend on (e.g. number of 1s
> and 0s, bit resolution)?

I think think the short answer is the bandwidth will be proportional to
the number of 1's and 0's per unit time.

-jim

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Thank you people for your suggestions and answers, I really do
appreciate the help.

I think I have a sense of what I am actually doing now that I played
around with it a bit in Matlab. The question that I was asking was I
feel complete nonsense. I generated simple pulse trains of different
combinations of 1s and 0s and just doing an FFT of them. There were
very little differences in the frequency response (if any) of the
different bit patterns (I tried extremes such as all 0s and only a
single 1 vs. consecutively varying 1s and 0s). I realized maybe there
would be a change in the frequency response if I modulated the PN
sequence onto the carrier. I saw that there were significant
differences in the frequency response as I tried different sequences.
If I am still wrong in my reasoning or somebody has another perspective
on the problem, please feel free!

Another thing that I would like to clarify is that I am trying to model
the power consumption of the individual blocks given in the transmitter
part of the CC2420. 

Thank You
Mohammed Billoo

billoo wrote:


> I am currently working on a project which involves determining the
> relationship between the the "bandwidth"(as my advisor puts it)  and
> power consumption of an I/Q transmitter. 

This might not be related to your question, but I have always
found the term "bandwidth" strange in describing digital signals.
(Specifically, data that is not the result of digitizing an
analog source.)

It is often used to described as bits/second, even on a parallel
bus.  If one considers a modulated carrier being used to
carry data, more bandwidth is required at a higher modulation
frequency, which really is bandwidth, assuming that the
modulation method is constant.  Quoting bandwidth in bits
per second, though, still seems wrong.  Even more, a bandwidth
in megabits/second is often written as Megahertz, even though
the modulation method might not be one to one.  (Or even one to
two including both upper and lower sidebands.)

(One description from some years ago included the bandwidth
of a car full of computer tapes.  That can be described
in bits per second or bits/time/distance when it is moving,
but there is no modulation, so a bandwidth seems wrong.)

-- glen

glen herrmannsfeldt wrote:
> billoo wrote:
>
>
> > I am currently working on a project which involves determining the
> > relationship between the the "bandwidth"(as my advisor puts it)  and
> > power consumption of an I/Q transmitter.
>
> This might not be related to your question, but I have always
> found the term "bandwidth" strange in describing digital signals.
> (Specifically, data that is not the result of digitizing an
> analog source.)
>
> It is often used to described as bits/second, even on a parallel
> bus.  If one considers a modulated carrier being used to
> carry data, more bandwidth is required at a higher modulation
> frequency, which really is bandwidth, assuming that the
> modulation method is constant.  Quoting bandwidth in bits
> per second, though, still seems wrong.  Even more, a bandwidth
> in megabits/second is often written as Megahertz, even though
> the modulation method might not be one to one.  (Or even one to
> two including both upper and lower sidebands.)
>
> (One description from some years ago included the bandwidth
> of a car full of computer tapes.  That can be described
> in bits per second or bits/time/distance when it is moving,
> but there is no modulation, so a bandwidth seems wrong.)
>
> -- glen

Bandwidth is an often abused term, but that said, any time variant
signal (i.e. not DC) has a bandwidth.

There are numerous distinct uses of the term (although they are, of
course, related ;)

The raw (burst) bandwidth of some channel such as a memory bus  or
indeed any information channel, although then we can look at
throughput, which is the effective bandwidth of the channel.

This is closely tied to the available bandwidth of the medium (be it
FR4, coax, free space or any other physical medium) which can limit the
bandwidth of the signal being applied, with the attendant distortion of
the signal.

Another usage is that of the actual or required bandwidth of a signal
and finds a lot of use in EMI/EMC discussions, antenna / filter design
and the like.

Being such a catch-all, it's important to get the context of the
discussion. In this case, the OP is being asked the relationship of
transmitter power to bandwidth, which really comes to a power density
issue, and each modulation type has it's own envelope vs. bandwidth,
which are always proportional (although the constant of proportionality
varies widely for different techniques, of course).

There's a huge amount to 'bandwidth', but as others have noted, the OP
in this case at least asked the question the 'right way'.

Cheers

PeteS