BUF802: Input impedance

Taketo Sato

Part Number: BUF802

Tool/software:

Hello team,

I have a question about input impedance information for BUF802.

its datasheet EC table says the input impedance is about 50Gohm//2.4pF at 100MHz. However figure 6-21 shows much different value. Is figure 6-21 information really correct?

Best regards,

3 months ago

+1 Ignacio Vazquez Lam1 3 months ago

TI__Genius 13585 points

Hi Taketo,

The value in the EC table is captured at DC. The reason you see this drop in input impedance across frequency is due to the 2.4pF input capacitance of the device. Page 23 in the datasheet highlights this idea and ways to account for this at the higher frequencies.

Best Regards,

Ignacio

0 Taketo Sato 3 months ago in reply to Ignacio Vazquez Lam1

TI__Genius 10215 points

Hello Ignacio-san,

Understood, thank you.

What is meaning of "f=100MHz" test condition for 50Gohm//2.4pF? I just curious.

Best regards,

+1 Ignacio Vazquez Lam1 3 months ago in reply to Taketo Sato

TI__Genius 13585 points

Hi Taketo-san,

That is a good question, this test condition is saying that this 50Gohm//2.4pF specification is valid at that frequency. If you look at the Figure 6-21, you can see this 50Gohm//2.4pF condition stays true in the region where the graph is linear before it starts really dipping in the 1GHz range. From 100MHz and below, this impedance stays true. Above 100MHz, the specification does start to change and 50Gohm//2.4pF is not true anymore.

Best Regards,

Ignacio

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BUF802: Input impedance