LMX2820: MUX_OUT_DOUBLER Issue in Fast VCO Mode

Hakan Yilmaz

Part Number: LMX2820

Hi Team,

I am using the LMX2820 in Fast VCO Calibration, Full Assist mode. I can switch between 5650-11300 MHz without any problems, but when I turn on MUX_OUT_DOUBLER above 11300 MHz, the signal is distorted in some areas. If I activate and write the DBLR_CAL_EN bit in R0 where these distorted areas, it was fixed (FCAL_EN = 0). This causes the calibration time to be extended. What do I need to do for if i am using MUX_OUT_DOUBLER in Fast VCO Calibration mode without any distorted areas?

Best regards.

over 4 years ago

0 Hakan Yilmaz over 4 years ago

Prodigy 20 points

Is it possible to access the tracking filter with a register. LMX2820 Datasheet mention it about this topic under the section of 7.3.9 Output Frequency Doubler, but i cant find any tracking filter register.

0 Noel Fung over 4 years ago in reply to Hakan Yilmaz

TI__Guru** 108130 points

Hi Hakan,

we don't have MUX_OUT_DOUBLER, which register were you trying to specify?

what do you want to find out with the tracking filter? The tracking filter is enabled with DBLR_CAL_EN=1. There is nothing configurable to the users.

0 Hakan Yilmaz over 4 years ago in reply to Noel Fung

Prodigy 20 points

I mean the OUTx_MUX = 2(VCO doubler) state on R78 and R79. Fast VCO Calibration, when doubler is on in Full Assist mode, I can't fast lock when I write DBLR_CAL_EN=1 bit on R0 register. My purpose is to run Fast VCO Calibration. Otherwise, the frequency lock time increases.

0 Noel Fung over 4 years ago in reply to Hakan Yilmaz

TI__Guru** 108130 points

HI Hakan,

If you can accept the sub-harmonic (i.e. the fundamental VCO frequency) in VCO 2x mode without enabling the tracking filter, you can make DBLR_CAL_EN=0.

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LMX2820: MUX_OUT_DOUBLER Issue in Fast VCO Mode