Part Number: TRF372017
I am using TRF372017 as a I/Q modulator to operate at 1.65GHz, According to datasheet, the OIP3 can be 25dBm at L band, and P1dB is about 11dBm.
But when I tested the OIP3 with two tone (150KHz space) on EVM board, and I can not get 25dBm OIP3, only around 20dBm at 0dBm output on our EVM board .
I do not know if the RF output of TRF372017 was matched to 50 ohm cross a wide band. and there is no impedance information on datasheet. on the EVM board, there is only a 22pF capacitor at the RF output.
As to OIP3, normally the output matching will affect OIP3 very much, Could you please tell the optimized matching impedance for OIP3 at 1.65GHz?
And are there any configuration setting in the chip to optimise OIP3?
Thank you very much!
In reply to Abdallah Obidat:
Thank you very much for your kind help!
One more question, Which one do you prefer to for the application at 1650MHz? TRF372017 or TRF3722?
In reply to jerry chen89:
I will test this in the lab. I'm assuming that your baseband signal of interest is still +/-75KHz, spaced 150kHz apart, is this correct?
Yes, please use +/-75KHz of the two-tone.
Also I notice that the return loss of RF output at 1800MHz is 6dB, Assume all the OIP3 data was gotten at 6dB return loss, which is very poor matching.
Then how will OIP3 change if the RF output is matched to 50ohm?
I’ve attached a plot of the worst case OIP3 for the TRF3722EVM. As the output power increases, the IM tones are higher in magnitude. In any case, the 1dB compression point is typically at 10.2 dBm for this device, so I would recommend staying below that to ensure linear operation. Nonlinear effects can observed at an output power of 5.5 dBm.
Also, this part, unlike the TRF3720, should show improved results by matching the output to 50 ohms. I suggest that you take a look at the TRF3722EVM schematic, to get a good starting point.
I was able to achieve 30 dBm, using the test conditions specified on the datasheet (Two tones, 1MHz separation, centered at 5MHz). As I mentioned earlier, I still believe that having your IM2, so close to your baseband signal and having it land on top of your second harmonic is bringing down your OIP3. I believe that if you were to increase your signal spacing and have them offset from DC you will see improved results. I’ve attached a screenshot of two tones at 1.125 MHz and 2.025 MHz, and a significant improvement can be observed.
Thank you for the detail test data!
Assume you test on the EVM board without any matching at 1650MHz, then the OIP3 is lower, we can see the OIP3 is about 23dBm at 0dBm output in the plots of OIP3 Vs Output power.
Do you mean the OIP3 will be improved to around 30dBm when the RF output is matched to 50ohm?
In the screen shot below,1. what are the spurs close to the main carrier? 2. why the upper side 3rd IMD is much higher than the lower side IMD?
It is expected to observe some asymmetry when measuring OIP3; in this case, this is partially suspected to be a limitation of the instrumentation used.
The spurs you see are the result of the third harmonic being modulated from baseband.
I don’t think that the main issue is caused by matching. The above capture was meant to illustrate that your issue stems from your baseband signal and that increased signal spacing, with an offset from DC would improve OIP3 significantly. The signal that you’d like to use isn’t offset from DC, which means your HD2 is falling on your IM2. Also, due to the relatively low frequency, IM4, IM5, etc… may no longer be insignificant and are also being modulated with your baseband signal.
You will probably see an improvement if you employ matching. But I think the solution would be to further space the signals apart and have them offset from DC.
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