xr2206 as a fsk modulator

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eoinitb
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xr2206 as a fsk modulator

Post by eoinitb » Mon Mar 21, 2005 2:36 am

Has anyone used the xr2206 or similar chip as a FSK modulator? I have followed the circuit exactly as per the datasheet bottom of page 9<p>http://www.exar.com/products/XR2206v103.pdf<p>i am getting no output from pin 2 the FSK output pin when the input is applied to pin 9. i have read on other forums of similar problems that I am having. Has anyone got this working is there anything additional I need that isn’t in the datasheet any advice would be greatly appreciated

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Edd
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Re: xr2206 as a fsk modulator

Post by Edd » Mon Mar 21, 2005 11:51 am

How is all in Eire;
Only, several years ago, when I was just using it just for its multiple waveform generating capability.<p>To check out its FSK operationality, initially , go to pin 11 and enable that stage by installing a 10k pull up resistor to Vcc and then monitor that VCO sync output to see if it then shifts its output in accordance with your
toggling of pin # 9 between its Hi-Lo states.
You didn’t specify your desired output waveform of the FSK data, I assume it to be a square if you are still in quest of your AC line communication.
Using the Da-Da sheet of the URL that you supplied and with a reviewing of the schematic of the internal chip circuitry on page 12 and its fig 15 depiction, I see no internal circuit path for the coupling of the VCO output info over into the intermediate waveshaping stages ( which also require external ancillary components) and/or the final buffers output which outputs at your specified pin 2, unless that VCO’s output gets fed into pin 3 (or 1,13 14.)<p>
73’s de Edd
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:D<p>[ March 21, 2005: Message edited by: Edd Whatley ]</p>

eoinitb
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Re: xr2206 as a fsk modulator

Post by eoinitb » Mon Mar 21, 2005 1:10 pm

the circuit i have built is as below it is from the datasheet i am getting absolutely no output from pin 2 Image

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sofaspud
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Re: xr2206 as a fsk modulator

Post by sofaspud » Mon Mar 21, 2005 2:17 pm

Except for the 0.1µF decoupling cap at Vcc the circuit is exactly like the datasheet. I'm stumped. Have you verified that you have valid inputs at pin 9? You suggest this is a known problem - might Exar have some online support that addresses the issue? Either with an app note or by email?
Just a couple of days ago, I was doing some inventory on my parts stock and found a XR2206. I hope the solution gets posted here so I can save it to my notes.

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Edd
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Re: xr2206 as a fsk modulator

Post by Edd » Mon Mar 21, 2005 7:01 pm

Repeating, to see if the FSK function is working:
“To check out its FSK operationality, initially , go to pin 11 and enable that stage by installing a 10k pull up resistor to Vcc and
then scope that VCO sync output to see if it then shifts its output in accordance with your modulating input into pin #9.”
Are you getting a responsive square wave at that test point ?<p>Also, if you will look at the the data sheets figure 11 it will show the VCO being internally connected to the buffer, while on other
figs, 12 13 14 it shows no interconnect, nor do I see it on the schematic of the IC on Fig 15. It does imply two lines on Fig 1
being interconnected, but I might only see it by a biasing interconnect via VR/V1/V2 in internal circuitry.
Also looking at the connection pin #3 on the external voltage circuit have you ran the pot thru its range while testing ?
At one end the trim-pot there would be an AC bypassing directly to ground thru the 10 ufd cap.
How about trying this arrangement on the pot, but just retain your same 5.1k divider resistor values.
:)

eoinitb
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Re: xr2206 as a fsk modulator

Post by eoinitb » Tue Mar 22, 2005 3:17 am

i see from your circuit your are using 12v as vcc i am only using 5 v should i be using 12. also what range of voltage should be going into pin 3

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sofaspud
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Re: xr2206 as a fsk modulator

Post by sofaspud » Tue Mar 22, 2005 7:26 am

The datasheet says the XR2206 minimum Vcc is 10V so yes try 12V.

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sofaspud
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Re: xr2206 as a fsk modulator

Post by sofaspud » Tue Mar 22, 2005 7:38 am

Also check the 50k pot at pin 3. On the datasheet schematic, the wiper is also connected to the voltage divider (1/2 Vcc). I see now on your schematic above it is only connected to ground through the 10µF capacitor.

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Re: xr2206 as a fsk modulator

Post by eoinitb » Wed Apr 06, 2005 8:38 am

thanks for your help guys i have kind of got it working <p>it seemes to produce the an output for logic 1 however when the input signal is logic 0 i am getting no output.see the oscilloscope scrren shot<p>
Image<p>has anyone experienced this problem before <p>any suggetsions

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Re: xr2206 as a fsk modulator

Post by Ron H » Wed Apr 06, 2005 9:55 am

According to the datasheet, minimum values for R1 and R2 are 1kohm.

eoinitb
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Re: xr2206 as a fsk modulator

Post by eoinitb » Wed Apr 06, 2005 11:49 am

sorry but where abouts in the data sheet does it say that

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Re: xr2206 as a fsk modulator

Post by Ron H » Wed Apr 06, 2005 1:40 pm

Page 4 under "recommended timing components".

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