PA/LNA control signal problem


the waveform in the upside of the picture is the dw1000 GPIO5 control signa. the bottom waveform of the picture is the signal while that get through the 1k ohm resistance to the mmbt3904.
Why in the second pic half of the waveform
is distortion.

If I saw a trace like that the first thing I’d look at is the quality of the ground connection on the scope probe. 90% of the time traces like that are poor equipment setup rather than genuine issues.

If the green trace is being driven via a 1k resistor the next things I’d look for would be cross talk introducing noise after the resistor or power supply noise.

hi Andy
thanks for your reply. I have checked the ground connection,the quality of the ground connection is ok,and GPIO5 control signal circuit is completely designed in accordance with aps006 product notes.
I 'm confused

The EXTTXE signal (GPIO5 when so configured) is not steady on during transmit by default. It pulses as you see above. This is called “fine grain sequencing”, which is the default behavior.

The EXTPA signal (GPIO4 when so configured) is steady on during transmit. We use EXTPA for our LNA/PA control for this reason and don’t use EXTTXE.

Another reason to use EXTPA is that it switches in advance of transmission to give the PA and RF mux time to settle so the preamble doesn’t get truncated. I don’t think EXTTXE does that.

APS004 and APS009 give further details. Specifically see PMSC_TXFSEQ register which can be used to turn off fine grain sequencing and get a more steady signal (user manual section 7.2.50.6).

Mike Ciholas, President, Ciholas, Inc
3700 Bell Road, Newburgh, IN 47630 USA
[email protected]
+1 812 962 9408

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Hi ,

i assume you are using BJT as inverter for this application. I have one doubt i dont know its true or not. If the transistor is not stabilized will it oscillate when transistor switched on.?

-Akhil

@mciholas

Was there no problem with using EXTPA (and nEXTPA) to both power on the PA and to switch between Tx and RX as described in APS009? I can find no timing information such as waveforms for GPIO4, 5 & 6 and measurement is no guarantee it will always be that way. I can imagine problems such as PA power-on causing the end of an Rx burst being lost, for example. Using only EXTPA would be very useful for us as I am modifying a very tight layout where bringing out fewer signals is highly desirable.