# Help to understand output levels of clock buffer

I'm dealing with clock buffer and trying to determine how output levels depends on the input. I'm using information from the datasheet. Here is the table with information:

I don't understand the information in this table completely. We see that output high voltage is measured at the certain conditions. The supply voltage is VDD=Min=1.65. The input voltage is VIH or VIL. I don't understand that. I expect the output voltage to be measured at the certain input voltage.

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Could you provide a link to the datasheet, please? –  Joe Hass Feb 23 '14 at 14:58
Here is the descriptive page. Press Download datasheet. –  zulunation Feb 23 '14 at 15:45
Sorry forgot to add a link pericom.com/products/clock-and-timing-ics/clock-buffers/… –  zulunation Feb 23 '14 at 16:45

A buffer for logic signals is very different from an analog amplifier.

With a logic buffer, you don't want the output voltage to depend on the input voltage; instead, you want it to output a logic high when the input is a logic high, and output a low when the input is low.

Therefore, the input specifications for the buffer indicate what voltage levels it considers to be high and low, and the output specifications indicate the capabilities of its drive circuit to output high and low under various load conditions.

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Specifically, the output voltage is guaranteed for the given load under any input that conforms to the $V_{IH}$ or $V_{IL}$ requirements, even the highest $V_{IL}$ or the lowest $V_{IH}$. –  Spehro Pefhany Feb 23 '14 at 15:26
So VOH will be at the output when the VIH is at the input. Please see the picture above. For the VOH there are conditions: VDD=MIN,its ok, VIN=VIH or VIL. That't not correct i think. There must be VIN = VIH –  zulunation Feb 23 '14 at 18:36
@zulunation There are two separate guarantees (and each of those at two currents). One set for the input high (VOH) and one set for the input low (VOL). Each guaranteed applies for any input voltage that is a valid VOH or VIL respectively –  Spehro Pefhany Feb 23 '14 at 20:08
I'm just trying to imagine how the measurements were done. For the VOH parameter from the table they set VDD to Min in our case it is 1.65V. Then they passed ViH to the input. In our case is is interval from 0.65*1.65V to 3.6V. Then they connected two loads. One gives 2ma another gives 8ma at the output. And they checked that for 2ma the Output voltage is 1.3V and for 8ma they checked 1.2 volts. Ok thats fine. But why did they mention ViL in the table. It is related to VOL measurements. –  zulunation Feb 23 '14 at 21:02