Hi TI,
We want to convert differential output to single ended using balun and will be connecting this output to SMA connector.
From the below images which configuration should we use?
1.
2.
OR if TI has some other configuration or modification in above images then please let us know.
What is the output frequency? Here are some suggestions:
ADT2-1T is one option. ADT2-1T-1P is another for higher frequency. For higher frequency consider the TC1-1-13MA+ as in (
) - note it is a 1:1 balun, so see note about impedance matching on liinked webpage.
ADTL2-18 also for high frequency.
73,
Timothy
Hi Timothy,
Thanks for the reply.
I have two more questions for you:
Question 1:
If I use 1:2 Balun, then can you please suggest how to do the connections of LMK04828 outputs to Balun, from the below attached images which is the right connections to make :
1.
2.
Question 2:
As per datasheet of LMK04828, Clkin pins should be terminated with 100 Ohms with AC coupling as per below diagram:
We are also using a 1:1 balun: MABAES0060 from M/A-COM , for converting the external refclk single ended input to differential to drive the clkin pins of LMK04828 as shown below:
Our refclk input frequency range is 10Mhz-100Mhz.
As shown above, balun is 1:1 so if input impedance of balun is 50 Ohm then output impedance is also 50 Ohm. And we have also placed a 100Ohm resistor across output of balun. So now impedance seen by ClKin pins is 33.33 Ohm(50ohm of balun in parallel with 100 Ohm resistor).
We have choose the 1:1 balun and placed 100Ohm resistor across output of balun , because we have taken the reference from ADC12DJ3200 Eval Board.
In Eval Board, to drive the CLKin pins , 1:1 balun (TC1-1-13M-23+) is selected and also 100 Ohm is placed across the output of balun. So I am assuming CLKin pins of LMK04828 in ADC Eval board, also sees the 33.33 Ohm impedance.
Eval Board schematic connections of 1:1 balun with LMK04828 clkin pins is shown below:
So our question:
Is it ok to use 1:1 balun and place 100ohm across balun output for driving CLKIN pins of LMK04828?
An early responese will be highly appreciated.
Thanks,
Lalit
LALIT VERMA said:1.
I suggest placing DC blocking capacitors between the emitter resistors R1 & R2 and the balun T1. Otherwise the impedance of the balun input is in parallel with the emitter resistors and this reduces the effective emitter resistor value.
LALIT VERMA said:2.
In this case, given a 50 ohm load at J2, then a 100 ohm DC load would be seen at input to T2. I do not see any reason for R4, it can be left open.
LALIT VERMA said:We are also using a 1:1 balun: MABAES0060 from M/A-COM , for converting the external refclk single ended input to differential to drive the clkin pins of LMK04828 as shown below:
Our refclk input frequency range is 10Mhz-100Mhz.
As shown above, balun is 1:1 so if input impedance of balun is 50 Ohm then output impedance is also 50 Ohm. And we have also placed a 100Ohm resistor across output of balun. So now impedance seen by ClKin pins is 33.33 Ohm(50ohm of balun in parallel with 100 Ohm resistor).
Since this is an input, I think you are considering this backward. The input doesn't need to see 100 ohms. The input needs to be terminated such that it does not reflect energy back to the driver. The LMK input is high impedance, traditionally you place the 100 ohms in parallel with the high impedance input buffer and have a 100 ohms differential load. When using a 1:2 balun, then the 100 ohm differential load looks like a 50 ohm single ended load. When using a 50 ohm source and a 1:2 balun, then the transmission line is properly terminated.
However, when using a a 1:1 balun 100 differential looks like 100 single ended to your 50 ohm source which is not good for matching and you will have reflections. In this case I simply recommend replacing R672 with a 50 ohm resistor. Now the 1:1 balun will present 50 ohms to the load. Your input amplitude will be less, but the transmission line will be properly terminated.
Note, that the MABAES0060 is not a traditional transformer type balun and does not provide a DC block. The schematic symbol for the balun is drawn incorrectly, refer to the drawing in the https://cdn.macom.com/datasheets/MABACT0060.pdf for the proper drawing.
LALIT VERMA said:In Eval Board, to drive the CLKin pins , 1:1 balun (TC1-1-13M-23+) is selected and also 100 Ohm is placed across the output of balun. So I am assuming CLKin pins of LMK04828 in ADC Eval board, also sees the 33.33 Ohm impedance.
I think they should have set R73 = 50 ohms.
LALIT VERMA said:Is it ok to use 1:1 balun and place 100ohm across balun output for driving CLKIN pins of LMK04828?
It is ok, however I recommend a 50 ohm resistor driving the CLKin pins.
I apologize for the late reply.
73,
Timothy
