• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 47 subscribers
  • Views 592 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

THS7530-Q1: Gain Error

cafain
Mastermind 6765 points
Part Number: THS7530-Q1


Hi,

Data sheet of THS7530-Q1 page7 Please tell me how to look at Figure2.

When VG+ = 0V　, Gain is 11.6dB (typ)
When VG+ = 0.9V, Gain is 46.5db (typ)
This is described in datasheet page5.
This value is a reference value, I understand that it is not guaranteed value.
(As it is typ)

page7 Looking at Figure2
When VG+ = 0V　, Gain is about  7dB (typ)
When VG+ = 0.9V, Gain is about 41dB (typ)
And you can judge by looking at the graph.
　　
When VG+ = 0V　, for the reference value of 11.6dB,→  7dB in the graph of Figure 2
Also
When VG+ = 0.9V, for the reference value of 46.5dB,→ 41dB in the graph of Figure 2

Q1.Why is there a big difference?

Q2.Also, the gain error is shown in Figure2 with Gain Error, but will Gain-Error fluctuate due to temperature change?

Q3.How is the individual difference (variation) of Gain-Error?

Q4.How is the individual difference (variation) of Gain?

best regards

  • 0
    TI__Genius 15975 points
    Hi Cafain,

    To answer your questions:
    1. The difference between the gain numbers in Figure 2 vs page 5 is that the Figure 2 gain is referred at the load of 50-ohms after the two 25-ohm differential series resistor (see Fig 16 in the datasheet), whereas the page 5 gain is the number directly at the amplifier differential output.

    2. Gain error is a subset of the actual gain being set at the Vg pin. Yes, the actual gain for a given Vg voltage will change across temperature which will eventually result in gain-error fluctuation due to temperature change.

    However, since the actual gain can be controlled by the Vg pin, you should be able to calibrate out the gain error by employing the VGA in automatic gain control (AGC) loop and look-up table. If you know the VGA gain at a given temperature of say 25'C and you were expecting G = x dB, you can accordingly adjust the Vg pin high or low depending upon the temperature increase or decrease. In this scenario, the delta error in gain would only result at the extremes of the Vg pin where the gain control loop runs out of range.

    3 & 4. I don't think we have any data taken to show the individual difference of gain/gain error for a given Vg voltage. You would have to take a lot of sample points in-order to statistically predict the gain error, and it wont be certainly applicable to individual part to part any ways. As mentioned in point 2, the benefit of VGA is that it lets you to correct for the gain error by employing the AGC loop. I would recommend you to employ it in-order to avoid any gain variation.

    Best Regards,
    Rohit