TPS99000-Q1: darkoffset trim

zhangyi yuan

Part Number: TPS99000-Q1

Hi there, we are working on DLP5530 system for ARHUD, and the picture below is the internal structure of the TPS99000 TIA part，

I want to know why do we need to - dark offset before Gain#2 and +back again after Gain#2 ?

over 1 year ago

0 Ross Schneider over 1 year ago

TI__Expert 3475 points

Hello -

Thank you for your question. Please note that the dark offset values are calculated automatically by the TI calibration algorithm.

Here is some more detailed information from our internal design documentation justifying the different gain stages:

"To cover high gain cases, TIA1 also includes an independent RGB set of dark current / offset correction parameters. This serves to add a pedestal to the input signal, so that the zero input current condition results in a stage 1 output voltage that is higher than 0V. This is needed to keep the downstream circuits working properly. The “darkoffset” correction function downstream serves to prevent stage 2 from applying gain to this input offset, so that stage 3 does not saturate due to high input offset."

Regards,

Ross

0 zhangyi yuan over 1 year ago in reply to Ross Schneider

Prodigy 60 points

Hi Ross, thanks for your kind reply.

As I guess, for blanking interval in a single frame, during calibration

TI's program will

1. Determine a gain for TIA1

2. set these 3 registers to composite TIA1 output to 0V

after steps 1, 2, we will make sure that the TIA1 output actually TIA1 = gain x PD current or TIA1=gain x light's on PD

actually dark offset trim, not only trim dark current, but it's the last parameter to make TIA1 output equal 0, at the same time, make Gain#2 working on a reasonable static working point

0 Ross Schneider over 1 year ago in reply to zhangyi yuan

TI__Expert 3475 points

Hello -

Please refer to this page for details on the calibration routine: https://e2e.ti.com/support/dlp-products-group/dlp/f/dlp-products-forum/1077842/faq-dlpc230-q1-dlp-auto-hud-gen-2-resources-and-documentation/3989125#3989125

Once you have a setup, these details will become more clear.

Regards,

Ross

0 Ross Schneider over 1 year ago in reply to Ross Schneider

TI__Expert 3475 points

Hello - I am planning to close this thread due to inactivity. Please reach out with additional questions.

Regards,

Ross

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TPS99000-Q1: darkoffset trim