# Cypress Developer CommunityTM

## can pulse shaping be done in PSoC3?

Summary: 4 Replies, Latest post by danaaknight on 03 Aug 2013 05:58 AM PDT
User
101 posts

Hi!

Can a positive tail pulse..amplitude no more than 5V and pulse duration maximum 50us (prf<= 1Mhz) be shaped to a gaussian near gaussian pulse using PSoC3?...Also like PSoC1 are the switched capacitor blocks available so that a simple CR-RC4 circuit can be realized?

Another thing...the block diagram of pulse oximeter on http://www.cypress.com/?rid=47829 shows an analog filter . I've not seen an analog filter in components of PSoC creator. How to find it?

User
7646 posts

"Can a positive tail pulse..amplitude no more than 5V and pulse duration maximum 50us (prf<= 1Mhz) be shaped to a gaussian near gaussian pulse using PSoC3?..."

See comments below on last item

"Also like PSoC1 are the switched capacitor blocks available so that a simple CR-RC4 circuit can be realized?"

www.cypress.com/

and take a look at this - www.cypress.com/

"Another thing...the block diagram of pulse oximeter on http://www.cypress.com/?rid=47829 shows an analog filter . I've not seen an analog filter in components of PSoC creator. How to find it?"

PSOC 3 has a digital filter block and DAC that can be used for general purpose filter. However your sampling rate

requirement of at least 2 Mhz (1 Mhz Nyquist preferably 10 Mhz Nyquist)  cannot be done because there is

no fast SAR A/D to keep up wirth sampling rate. OpAmps could be used for filtering, but their GBW of 3 Mhz

too low to implement a meaningful repeatable filter at 1 Mhz.

Regards, Dana,

User
1362 posts

Due to the central limit theorem, the Gaussian can be approximated by several runs of a very simple filter such as the moving average. The simple moving average corresponds to convolutionwith the constant B-spline ( a rectangular pulse ), and, for example, four iterations of a moving average yields a cubic B-spline as filter window which approximates the Gaussian quite well.

With pulse width of 50us, moving average filtering is doable, with 1mhz sampling  ADC and DMA

User
9281 posts

...and even the moving average can be done in hardware by using the UDBs programmed in Verilog and using a datapath could enforce the performance.

Bob

User
7646 posts

The max sampling rate of Delsig, occuring at its lowest resolution, 8 bits, is 384K SPS,

16 bits at 48KSPS. PSOC 3  is limited to DelSig.

en.wikipedia.org/wiki/Gaussian_filter

The DFB block in PSOC 3/5 can be used to implement a FIR based Gaussian

approximation. Some design help can be found at -

www.mathworks.com/help/signal/examples/fir-gaussian-pulse-shaping-filter-design.html

Google "fir gaussian filter", there are a number of tools, some free, that can help

determining the coefficients for a FIR solution.

IIR approach - www.cwp.mines.edu/Meetings/Project06/cwp546.pdf

Regards, Dana.