Additive Synthesis after bandpass filter

Tip / Sign in to post questions, reply, level up, and achieve exciting badges. Know more

cross mob
Anonymous
Not applicable

Dear all,

   

I want to do additive synthesis (or harmonic synthesis of sine wave).
I use the solution filtering (band pass filtrer) to generate sine waves with timer 8 bits
on a PSOC1 Model CYC8C29466.
I create two harmonic signals (different frequencies, different amplitudes)
and I want to add these two analog signals.

   

What do you propose of solutions ?

   

Hardware ?

   

Software ?

   

Thank you very much for your propositions

0 Likes
3 Replies
Bob_Marlowe
Level 10
Level 10
First like given 50 questions asked 10 questions asked

Easiest seems to be to route the two signals to pins and add them with a simple resistor network.

   

 

   

Bob

0 Likes
DennisS_46
Employee
Employee
100 sign-ins 50 likes received 50 solutions authored

Bob's right, the easiest way is two filters and a resistive adder externally. Feed back into a PGA to get a buffered low-impedance output. You could put a cap on the resistor summing junction to filter out most of the sampling aliases.

   

IF . . . . you want zero external parts. Put one LPF in ASC10, ASD11, feed filter from digital input on P2[1]. Put second LPF in ASC23, ASD22, feed filter from digital input on P2[2]. Sum the outputs with an MDAC6 in ASC21; you'll have to set the B-input on block ASC21 in your code. Cool part this way is that you can scale the levels by changing the A and B caps. This results in levels that are dependent on power supply. If you want absolute levels, connect filter inputs to RefHi, then modulator bits to your digital signals. Set RefHi to something other than Vdd. You'll get the best result if the filters have the same column clock.

   

IF . . . . you are software-centric you can follow the method of the DTMF dialer user module and do with direct digital synthesis into a DAC. This is probably limited to a few kHz.

   

The limit on your output frequency is the slew rate of the analog column output buffer, roughly 40 kHz for rail to rail swing with no distortion caused by slew rate limiting.

0 Likes
ETRO_SSN583
Level 9
Level 9
250 likes received 100 sign-ins 5 likes given

If this is DTMF or CTSS, there is a module for former, and an ap note

   

for latter - http://www.cypress.com/?rID=2600

   

 

   

Or you could always adapt DTMF module for different tone set.

   

 

   

And of course implment DDS approach http://www.sdiy.org/kbadc/dvco.html

   

 

   

Regards, Dana.

0 Likes