Re: si5351 crosstalk #radiuno

Hans Summers

Hi Glenn

> Right now, the only way i can see to use multiple 
> (10pin) Si5351's in a rig is to have say, an ATtiny or
> similar 8 pin uP to program it on power up. Or as
> commanded by the master uP.

It is not difficult to program a second (or third etc) firmware-emulated I2C port on the microcontroller. The inbuilt I2C/TWI peripheral isn't the only way to do it. I have code examples in the pages below

This way, you can program multiple Si5351A from the same microcontroller. You need only one additional I/O pin per device since all Si5351A can share the same SDA pin. Only SCL needs to be unique per device. 

However in my opinion this is a somewhat complicated solution to the problem. 

In many situations there is NO problem. You may not be using multiple Si5351A outputs concurrently. The spurs may not be on frequencies that matter, in the design. Or the spurs may be at a neglible level.

The last point is important. The spurs are worse the lower the impedance of the load on the Si5351A outputs. I think that this is entirely expected within chip, but it is very nice to see it quantified.

The easy solution is don't load the outputs heavily. Use a buffer with a high impedance input. Then the spurs disappear into the noise floor. In most cases this solution is probably cheaper and easier than multiple Si5351A.

73 Hans G0UPL 

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