• TI Thinks Resolved

TRF372017: Low power output from modulator, only see -20dBm instead of +5dBm.

Part Number: TRF372017

Register dump:

# Sequence 1, 2, 5, 6, 7, 4

Reg1: 0x91000806,
Reg2: 0x50B20510,
Reg5: 0xB145C0B0,
Reg6: 0x700809A9,
Reg7: 0xF008820B,
Reg4: 0x30018052

(11:21:42) TX: 1002040137910036
(11:21:42) RX: 1002048137910036
(11:21:42) TX: 10020401380806B8
(11:21:42) RX: 10020481380806B8
(11:21:42) TX: 100204013750B2C4
(11:21:42) RX: 100204813750B2C4
(11:21:42) TX: 1002040138051010B1
(11:21:42) RX: 10020481380510B1
(11:21:42) TX: 1002040137B145D0
(11:21:42) RX: 1002048137B145D0
(11:21:42) TX: 1002040138C0B055
(11:21:42) RX: 1002048138C0B055
(11:21:42) TX: 100204013770084F
(11:21:42) RX: 100204813770084F
(11:21:42) TX: 100204013809A914
(11:21:42) RX: 100204813809A914
(11:21:42) TX: 1002040137F008CE
(11:21:42) RX: 1002048137F008CE
(11:21:42) TX: 1002040138820B39
(11:21:42) RX: 1002048138820B39
(11:21:42) TX: 1002040137300196
(11:21:42) RX: 1002048137300196
(11:21:42) TX: 10020401388052F3
(11:21:42) RX: 10020481388052F3

Modulator I and Q inputs set to zero.

  • If you are using the TI GUI you can send a screen shot of the front page where it is easier to see the controls. Here are a few things to check:

    1. Make sure you are looking at the proper sideband. The spectrum may be reversed from what you are expecting and you may be looking at the suppressed sideband.

    2. It is stated modulator inputs are zero. That implies no signal. If there is no BB signal then there is no RF output except...

    3. LO feedthrough comes to the output. It should be around -40 dBm. Verify that this is not the signal you are seeing.

    4. Verify the BB signal is set with Vcm = 1.7V or AC couple and use the internal Vcm generator.

    5. Verify the LO signal is locked and at the proper frequency.

    6. Check soldering of the output SMA connector; solder joint may be damaged / cracked.

  • In reply to RJ Hopper:

    Yes, about -40 dBm is what we are seeing. So this would be normal then, since the IQ multiplers need more than a zero input to increase the RF Output above -40 dBm?


  • In reply to Val Martin:

    Yes, you are seeing the carrier feed-through at programmed LO (~1575 MHz). This is normal. The carrier feed-through is not the "normal RF output". The carrier feed-through is the product of small DC-offset mismatch in the I/Q baseband input. Now, you are not injecting any I/Q input so there is no RF signal output. The internal I/Q DC offset mismatch is generating the carrier feed-through you see on the S/A.

    If you inject, say, a 5 MHz BB tone, then you should see the RF output 5-MHz away from the carrier and a suppressed image 5 MHz away in the other direction.