# AD8351 input / output common voltage range ?

Hi all,

we are confused about input / output common voltage & input / output range !

Please let me know, which is correct.

In the datasheet, following is it.

specifications

INPUT/OUTPUT CHARACTERISTICS
Input Common-Mode Voltage Adjustment Range 1.2 to 3.8 V typ
Max Output Voltage Swing 1 dB compressed 4.75 V p-p typ

Pin Function Descriptions

INHI Balanced Differential Input. Biased to midsupply, typically ac-coupled.
INLO Balanced Differential Input. Biased to midsupply, typically ac-coupled.

VOCM Voltage applied to this pin sets the common-mode voltage at both the input and output. Typically decoupled to ground with a 0.1 μF capacitor.

The common-mode output voltage level can be adjusted from 1.2 V to 3.8 V by driving the
desired voltage level into the VOCM pin

Q1

What is input common voltage range?

What is input range & AMR about input pin ?

Q2

What is output common voltage range?

Q3

What is true function about Vocom pin ?

Q4

Can you provide the example of a single-ended-to-differential, dc-coupled, INHI input circuits w/ AD8351 ?

Best regards,

sss

edit
[edited by: sss@jpn at 7:01 AM (GMT 0) on 1 Nov 2019]

## Top Replies

• I'm not an expert on AD8351 but I'll try to respond to your questions:

Q1

What is input common voltage range?

What is input range & AMR about input pin ?

Parents
• Hi sss_4000_jpn,

I'm not an expert on AD8351 but I'll try to respond to your questions:

Q1

What is input common voltage range?

What is input range & AMR about input pin ?

Response: AD8351 is essentially meant to be operated AC-coupled. The inputs (INHI and INLO) are self-biased to mid-rail. As far as VOCM is concerned, the 1.2V to 3.8V range applies.

The absolute maximum ratings for the input(s) is not specified. It is common to limit these voltages to less than one diode drop (about 0.25V over temperature) above VPOS and to below GND.

Q2

What is output common voltage range?

Response: With VCOM set to mid-rail, 4.75Vpp (2.38Vpp on each output) will be the output voltage swing capability for 1dB compression. As VOCM is varied from mid-rail, this will cut into the output swing capability.

Q3

What is true function about Vocom pin ?

Response: The input / outputs pins bias to the voltage applied to this pin. This is very useful when using the AD8351 to drive an ADC, as shown in Figure 40 by tying the ADC VREF to VOCM.

Q4

Can you provide the example of a single-ended-to-differential, dc-coupled, INHI input circuits w/ AD8351 ?

Response: I don't think AD8351 is suitable for single ended to differential dc-coupled applications. Here are some DC coupled devices that can do the single ended to Diff conversion for you:

LTC6409

etc.

SE to diff devices Parametric Search Table:

https://www.analog.com/en/parametricsearch/11157

Regards,

Hooman

• Hi sss_4000_jpn,

I'm not an expert on AD8351 but I'll try to respond to your questions:

Q1

What is input common voltage range?

What is input range & AMR about input pin ?

Response: AD8351 is essentially meant to be operated AC-coupled. The inputs (INHI and INLO) are self-biased to mid-rail. As far as VOCM is concerned, the 1.2V to 3.8V range applies.

The absolute maximum ratings for the input(s) is not specified. It is common to limit these voltages to less than one diode drop (about 0.25V over temperature) above VPOS and to below GND.

Q2

What is output common voltage range?

Response: With VCOM set to mid-rail, 4.75Vpp (2.38Vpp on each output) will be the output voltage swing capability for 1dB compression. As VOCM is varied from mid-rail, this will cut into the output swing capability.

Q3

What is true function about Vocom pin ?

Response: The input / outputs pins bias to the voltage applied to this pin. This is very useful when using the AD8351 to drive an ADC, as shown in Figure 40 by tying the ADC VREF to VOCM.

Q4

Can you provide the example of a single-ended-to-differential, dc-coupled, INHI input circuits w/ AD8351 ?

Response: I don't think AD8351 is suitable for single ended to differential dc-coupled applications. Here are some DC coupled devices that can do the single ended to Diff conversion for you:

LTC6409