input impedance; wide-band amplifier

[beaver]

wideband amplifier

Hi, everyone!

Is a low impedance a feature of wide-band amplifier? Take AD603 for example, the input impedance is 100Ω. And in the configuration provided in the datasheet, the input impedance is set to be 50Ω. Can anybody tell me why?

Thank you in advance.

 

[Joatt]

calculate impedance input of an amplifier

50-Ohms input impedance is very common in RF components for impedance matching purposes. Testing equipment such as Network Analyzers an Spectrun Analyzers use 50-Ohms connectors. Furthermore, 50-Ohms coaxial cables are well-known and widely used. By satisfying the impedance matching at the input of the amplifier, you minimize the loss in your signal.

Regards

 

[FvM]

what is input impedance of an amplifier

These are two different points:

- Why impedance matching (typically 50 ohm) is used in RF and wideband pulse signal connections?

- Why has AD603 100 ohm input impedance.

For the first point, you should consider, why it's the only way to distribute these signals undisturbed through cable connections (or more exactly, transmission lines).

The second point is simple. AD603 is a VGA rather than a simple amplifier. 100 ohm is the input impedance of the attenuator network. You may want to consult the data sheet.

You usually find wideband amplifiers with fixed 50 ohm input and output impedance when you go to the GHz and above domain. That's (among other reasons) due to to the fact, that external termination resistors won't achieve sufficient wide band impedance matching.