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PLL Interface - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


RFguy
Post subject: PLL interface Posted: Wed Dec 28, 2005 9:15 pm
Who can give advice for PLL interface:
if PLL divders and powerdown setting are programmable through a three-wire serial interface, for a fixed frequency operating, can I use a simple three-wire series EEPROM instead of microcontroller for PLL interface.
Your kind help will be greatly appreciated


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IR
Post subject: Posted: Thu Dec 29, 2005 2:07 am

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello RFguy,

Yes you can use EEPROM for that. The PLL chip doesn´t really care about the way the programming command is being provieded, as long as it provided in the right sequence, timing and logic levels.

_________________
Best regards,

- IR


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Guest
Post subject: PLLPosted: Thu Dec 29, 2005 8:12 am
Most if not all EEPROMs are not system controllers. A "system controller" is capable of generating control signals. That means that most if not all EEPROMs cannot be used to generate the control signals needed by the PLL. You'll need a microcontroller or PLD to do that.

EEPROMs merely respond to "read" and "write" commands generated elsewhere.

Good Luck!


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RFguy
Post subject: Posted: Thu Dec 29, 2005 5:47 pm
Thanks for guest and IR. Does it mean I should use microcontroller such
as ATMEL ATtiny22, not use a simple three-wire serial EEPROM such AT93C86?
Regards,


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RFguy
Post subject: Posted: Thu Dec 29, 2005 6:05 pm
Sorry, another question: if PLL frequency is fixed, does it still need any microcontroller or EEPROM? May it can be programmed outside from PC?
Thanks.


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Guest
Post subject: Posted: Thu Dec 29, 2005 6:43 pm
Hello again RFGuy,

The EEPROM is needed to program your PLL to hope from one known fixed frequency to another. In case that your frequency is constant and doesn´t vary at all, you can program your PLL without any EEPROM or any other PLD or µP.

Good luck!


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RFguy
Post subject: Posted: Thu Dec 29, 2005 7:20 pm
Thank you. Guest. You are so kind. It means even I don't need to put any EEPROM or uP in the RF board. Right?


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IR
Post subject: Posted: Fri Dec 30, 2005 1:14 am

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello RFgUy,

That is true. If you use only a single constant frequency then you can deliver your signals directly to the PLL without any additional components.

_________________
Best regards,

- IR


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Guest
Post subject: PLLPosted: Fri Dec 30, 2005 1:43 am
IR & RFguy,
It depends on the specific PLL chip. Those that have a 3-wire interface such as I2C (Philips) or SPI (Motorola/Freescale) and including many by National, must have some circuitry to provide serial data and clock. IR is correct, IF and ONLY IF you have a parallel interface PLL chip, or one of the very rare ones with on-board EEPROM. So be careful - just because you need only one frequency does not mean that you don't have to get the correct divisor(s) into the chip.

Good Luck!


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RFguy
Post subject: Posted: Fri Dec 30, 2005 2:11 pm
Guest and IR,
Thank your help. How about Silicon Lab Si3133 or Si4136? it has 3 -wire serial interface. No need extra components?
Happy New Year


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Guest
Post subject: PLLPosted: Sat Dec 31, 2005 8:01 pm
I think you require external parts with the SiLabs Si4136. According to the data sheet:
The Si4136 is programmed serially with 22-bit words
comprised of 18-bit data fields and 4-bit address fields.
When the serial interface is enabled (i.e., when SEN is
low) data and address bits on the SDATA pin are
clocked into an internal shift register on the rising edge
of SCLK. Data in the shift register is then transferred on
the rising edge of SEN into the internal data register
addressed in the address field. The serial interface is
disabled when SEN is high.

Which sounds to me like there are no dependable default values loaded in.

IR, do you read it the same way?

Good Luck!


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RFguy
Post subject: Posted: Sat Dec 31, 2005 10:03 pm
Thank guest. You helped me many times. Before that, I did PLL design only for loop filter and VCO, the frequency is not fixed, so always used microcontroller , but no direct design with control function. so I am not good at PLL interface. if frequency is fixed, Si4136 need microcontroller or not? welcome more advices from PLL expert


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Guest
Post subject: Need to pay attention to sink/source currentsPosted: Sun Jan 01, 2006 9:24 am
Regardless of what you use for a controller, you will need to check the sink/source current requirements for the PLL control lines. I found out about this minor, but important, detail the hard way in one of my former designs.


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IR
Post subject: Posted: Sun Jan 01, 2006 10:14 am

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello RFguy and guest,

Indeed you will need control over the timing of writing to the Si4136.
In the designs I have been involved with, it was done through a CPLD.
The function of the CPLD is to assure the right timing of the writing sequence to the PLL device.

Also using CPLD makes it easier for you to debug the circuit in case of problems. Most often it happens that bits are sent in a wrong order because of misunderstanding the sequence mentioned in the data sheet.
Then while getting a strange output frequency or none at all, one can´t really understand if the problem is programming-related or RF-related. By using a CPLD or similar programmable device it is easier to eliminate and tackle problems.

_________________
Best regards,

- IR


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RFguy
Post subject: Posted: Sun Jan 01, 2006 11:47 am
Thank IR and guest again. Have a wonderful new year!



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