Hello,

I will use the AD8015 for my design, there is a datasheet detail that I don't quiet understand and I don't have a SPICE model neither the real part to check right now.

My questions are about the AD8015's differential output (cf. AD8015 datasheet, REV. A, page -2-) :

1) I can see that the Output Voltage Swing is almost divided by 2 when it's 50 Ohm loaded/adapted, why it is equal to 600mVpp and not 1Vpp/2 = 500mV refer to the High Impedance (Rl = infinite) measurement ?

2) I power the cheap up by applying +5V on +Vs (pin 8) and 0V on -Vs (pin 5), so the Output Common Mode Voltage is supposed to be 5 - 1,3 = +3,7V ? for High Impedance Load or 50 Ohm Load ? Is - it auto adjustable and always equal 3,6V no matter the load, or is it divided by two when adapted, or divided by two plus something unknown in the document (like the voltage swing case) ?

Thank you for your answer !

Dear Mathison,

Thank you for being interested in AD8015.

Here are our answers to your important questions:

1) I can see that the Output Voltage Swing is almost divided by 2 when it's 50 Ohm loaded/adapted, why it is equal to 600mVpp and not 1Vpp/2 = 500mV refer to the High Impedance (Rl = infinite) measurement ?

Differential Voltage Swing into RL = infinite is derived from the max. input current range data, confirmed by using DC evaluation board.

Differential Voltage Swing into RL = 50ohm is measured at 100MHz using a HP8656A signal generator to drive the input of an AC evaluation circuit, while a Tektronix 11402A Digitizing Oscilloscope monitors the outputs.

These data came from different test evaluation setups, so they have no direct 1/2 ratio correlations.

2) I power the cheap up by applying +5V on +Vs (pin 8) and 0V on -Vs (pin 5), so the Output Common Mode Voltage is supposed to be 5 - 1,3 = +3,7V ? for High Impedance Load or 50 Ohm Load ? Is - it auto adjustable and always equal 3,6V no matter the load, or is it divided by two when adapted, or divided by two plus something unknown in the document (like the voltage swing case) ?

Yes, the typ. common mode voltage, at your +5V single ended supply setup, should be +3.7V.

This is the process of how to evaluate the common mode voltage:

Each output of the DC evaluation circuit is measured with a HP34401A meter relative to +Vs. The AD8015 is operating under nominal supply and typ. temperature conditions with zero input current.

Please contact me at dongfeng.zhao@analog.com to get the details of the AC/DC evaluation circuits.

Best Regards,

Dongfeng