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Posts: 3
Registered: ‎04-28-2015
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Si5xx-5x7-EVB or Si5xx-PROG-EVB as a programmable frequency generator? New freq. every apx. 1 mSec?

Can I use a Si5xx-5x7-EVB or a Si5xx-PROG-EVB evaluation board, with suitable device mounted, as a programmable frequency generator, driven by an embedded microprocessor, such as an Atmel (Arduino), PIC, etc.? I want to change the frequency every few milliseconds, so as to step through a range of frequencies, such as 1 MHz to 150 MHz, or a subset of this range.

 

The application is an antenna analyzer, in which the signal from a frequency generator is fed to a resistive bridge, with the antenna connected as one leg of the bridge. Rectifying (detecting) voltages at two points in the bridge enables measuring strength of a signal fed to the antenna and strength of a signal reflected back from the antenna, thereby enabling calculating voltage standing wave ratio (VSWR), which is a figure of merit of the antenna and feed line. Minimal power (only a couple of milliwatts) is needed. A direct digital synthesizer (DDS), such as AD9850 would work, but does not have the frequency range I seek.

Posts: 19
Registered: ‎11-21-2014

Re: Si5xx-5x7-EVB or Si5xx-PROG-EVB as a programmable frequency generator? New freq. every apx. 1 mS

Hi,

Yes, it is possible to use your own microprocessor to drive one of our devices through our board.

 

I would recommend using the the Si5xx-PROG-EVB as the current hardware supports I2C communication, while the Si5xx-5x7-EVB does not.

 

On the Si5xx-PROG-EVB, there are two points where you can patch in your microprocessor's I2C commands. The first is done before the I2C Level Translators (PCA9306) and the second is after.

 

For the first patch point, you can remove the J20 jumpers and attach your I2C leads. The I2C commands will then be sent through a I2C Level Translator adjusting the voltage levels according to the DUT's supply voltage.

 

The second patch point uses TP4(SDA) and TP8(SCL), which will bypass any level translation.

 

Below is a link to the Si5xx-PROG-EVB user guide.

 

http://www.silabs.com/Support%20Documents/TechnicalDocs/Si5xx-PROG-EVB.pdf

 

Regards,
Matt

Posts: 3
Registered: ‎04-28-2015

Re: Si5xx-5x7-EVB or Si5xx-PROG-EVB as a programmable frequency generator? New freq. every apx. 1 mS

Dear Matt:

 

Terrific! Thank you very much.

 

I see the Si5xx-PROG-EVB board supports several devices (Si514, Si570/571 and Si598/599). Do you recommend any one of these in particular for my application?

 

Best regards,

George

Posts: 48
Registered: ‎02-24-2014

Re: Si5xx-5x7-EVB or Si5xx-PROG-EVB as a programmable frequency generator? New freq. every apx. 1 mS

George,

 

Sorry for the late reply, but adding some info here for anyone else that is looking for advice.

 

The I2C programmable oscillators have different performance levels for generated low-level spurs, but all will work fine for this application. Here the XO and VCXO part numbers are ranked as 'good' 'better' and 'best':

 

Si570 best XO

Si571 best VCXO

 

Si598 better XO

Si599 better VCXO

 

Si514 good XO

 

The Si514 has a simpler programming interface than the Si57x and Si59x and it is smaller and less expensive, so that is often the first choice for a programmable XO.

 

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Posts: 3
Registered: ‎04-28-2015

Re: Si5xx-5x7-EVB or Si5xx-PROG-EVB as a programmable frequency generator? New freq. every apx. 1 mS

Thank you very much for the additional information. I am, however, still a bit confused by the difference between an XO and VCXO. It seems an XO is a fixed-frequency crystal oscillator, whereas a VCXO is a voltage-controlled oscillator. Can I use an XO in a Si5xx-PROG-EVB board to generate signals whose frequencies are established programmatically by my microprocessor? Or, must I use a VCXO in this case?

 

Or, am I completely missing the point. In other words, is the XO or VCXO used simply as a frequency base by the Si5xx-PROG-EVB to generate signals of any programmatically selected frequency?

 

Best regards,

George