### Krishna Murthy (@flutekick)

Working as a Design Engineer in the DSP team at Analog Devices, India

## Re: Estimating SNR in the Frequency Domain

I didn't say it is a must. If you choose your signal on bin, finding SNR is straightforward.

## Re: Estimating SNR in the Frequency Domain

Does your signal exactly fall on bin?

## Noise aliasing with CIC filter

Hi,Would the amount of noise aliasing/folding back into signal band change as we change decimation ratio of the CIC filter. (Assume the input has white noise)In...

## Re: SNR measurement with fixed-point FFT

I didn't get what you meant by "Regardless, if you are using the same input data for both your cases the sample length is irrelevent."Also, what is trivial data?...

## Re: SNR measurement with fixed-point FFT

Hi dszabo,Thanks for your reply.Yes, input data is from ADC. I think 128-point should be sufficient to find the SNR unless you want to find some spurs, in which...

## Re: SNR measurement with fixed-point FFT

What are the internal bit-formats?

## Re: SNR measurement with fixed-point FFT

Hi Kaz,Yes, thats correct.Thanks,Krishna

## Re: SNR measurement with fixed-point FFT

The rand() function in matlab returns only positive values from (0,1). Right? or Am I missing some other function which could generate zero mean random noise.So,...

## Re: SNR measurement with fixed-point FFT

I expect the ADC ENOB to be ~12bits. To model the thermal noise, I have just used rand function with dc offset removed.I am concerned about why the fixed-point FFT...

## Re: SNR measurement with fixed-point FFT

Hi Artmez,Thanks for the reply. My input data is from output of ADC including the thermal noise. Also, the tone is placed on bin. So, the SNR is not really SQNR...

## SNR measurement with fixed-point FFT

Hi,I measured the SNR of an input signal with full precision and 16-bit fixed-point precision FFT in matlab.The full precision resulted in 69dB SNR, but the fixed-point...

## Re: Fixed-point FFT scaling

Thanks a lot. But this is true only if the signal in not on bin, right?If my input tone is placed on bin and I want to measure the SNR, then the gain should be N,...

## Re: Fixed-point FFT scaling

Why is the gain dependent on my input tone?

## Fixed-point FFT scaling

Hi,I have seen other discussions on this topic in this forum. But I am still not too clear on this.Here is my understanding : Basically, the need for scaling FFT...

## Re: Goertzel algorithm

Thanks Tavassoli.I am just wondering if DFT/FFT and Goertzel evaluates the same bin, why should Goertzel depend on additional sample?

## Goertzel algorithm

Hi,For Goertzel algorithm, does it require N+1 or N samples to generate the bin corresponding to N-point DFT?In Rick's book I see the following statement "For the...

## Re: Magnitude of frequency components

Hi,You might want to try Goertzel algorithm and get the estimate of mag/phase of the bin you are interested in.CheersKrishna

## Re: Back to back CIC filters

It works perfectly fine, if I operate the first stage integrator also with the same bit-width as the last stage differentiator.

## Re: Back to back CIC filters

Hi Rick,Wouldn't that be equivalent to (1-z^-AB)/(1-z^-1) from the simplied diagram I have posted earlier?Krishna

## Re: Back to back CIC filters

Tim,Absolutely. I was thinking the same, the bit-widths need to be same between integrators/differentiators. Hence, in theory what I have shown might make sense...

## Re: Back to back CIC filters

Hi Chris,Could you help me with what is wrong with the math? Atleast what i was referring to is given below with simplied diagram. Let me know what is wrong in the...

## Re: Back to back CIC filters

The second integrator operates at the same rate as the differentiator of the first stage. So, the 1/(1-z^-1) is infact 1/(1-z^-R1).

## Re: Back to back CIC filters

Hi cfelton,I am talking about the differentiators of the 1st stage and integrators of 2nd stage. Isn;t itÂ (1-z^-1)^3/(1-z^-1)^4 ?Krishna

## Re: Back to back CIC filters

Hi Stephane,Thanks for pointing out. I have uploaded them now.Krishna

## Back to back CIC filters

Hi,If I have to design a decimation filter for a 4-bit sigma-delta ADC, decimation factor say 6, I plan to split the filter into 2 stages of CIC filtering (first...

## Re: Can we paralleize the integrator stage of CIC?

In my case, I want the decimation ratios to be programmable. In a CIC, one need not design the filter again for different decimation ratio. But it is not the case...

## Re: Can we paralleize the integrator stage of CIC?

Exactly Dave. CIC polyphase doesn't make much sense.

## Re: Can we paralleize the integrator stage of CIC?

Dave,But polyphase for CIC would mean I can no longer implement a integrator/comb structure? I mean to say each of the polyphase would now look more like a regular...

## Re: Can we paralleize the integrator stage of CIC?

Hi gretzteam,Thanks a lot for the comments. I am using the integrator with the delay in the forward path, so no issues there. But I further want to reduce the frequency...

## Can we paralleize the integrator stage of CIC?

Hi,Since, the integrator stage of #CIC operates at higher frequency compared to differentiator, it becomes critical for timing in a high-speed design. Is there a...

## Re: How to estimate the SNR

Hi Chess,I believe SNR measurements for a system is always done with a single tone input and the procedure mentioned by you works fine for a single tone.Please correct...

## Re: Polyphase CIC structure

Hi Tim,Thanks for your reply. I have implemented CIC too in my system for the sigma-delta ADC. But is any implementation available for the same where data is coming...

## Re: Polyphase CIC structure

Rick,Thanks for the reply and the materials provided.Also, sorry for not being clear with my question.I am yet to go through the links you have provided, but what...

## Polyphase CIC structure

Hi,Any pointers to implementation of polyphase #CIC decimation filter implementation?Thanks,Krishna

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