Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

low input impedance of amplifer

Status
Not open for further replies.

jimmykk

Full Member level 2
Joined
Oct 2, 2014
Messages
124
Helped
0
Reputation
0
Reaction score
0
Trophy points
16
Activity points
1,260
I have a question regarding the input impedance of amplifier AD605 . It has an input impedance of 175 Ohm while output Impedance is 2 Ohm.
Why is it having such a low input impedance ....shouldn't it be in the range of kOhmS or MOhms
 

jimmykk

Full Member level 2
Joined
Oct 2, 2014
Messages
124
Helped
0
Reputation
0
Reaction score
0
Trophy points
16
Activity points
1,260
I think you are talking about the input resistance provided by the gain control interface ....isnt it different from the actual input resistance of the amplifier.

 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
48,418
Helped
14,251
Reputation
28,763
Reaction score
12,940
Trophy points
1,393
Location
Bochum, Germany
Activity points
280,187
Why is it having such a low input impedance ....shouldn't it be in the range of kOhmS or MOhms
Did you eventually read the datasheet? The differential inout goes to the attenuator ladder rather than an amplifier.
 

jimmykk

Full Member level 2
Joined
Oct 2, 2014
Messages
124
Helped
0
Reputation
0
Reaction score
0
Trophy points
16
Activity points
1,260
Sorry.....but can you please explain about the attenuator ladder what does -48db means here.......and what is the actual input impedance offered by the amplifier
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
48,418
Helped
14,251
Reputation
28,763
Reaction score
12,940
Trophy points
1,393
Location
Bochum, Germany
Activity points
280,187
As the block diagram shows, there's no direct access to the differntial amplifier input. Instead a differntial ended attenuator network with 175 impedance is connected in front of it. The attenuation can be programmed between 0 and 48 db via VGN control voltage. I imagine that each ladder node drives a differential pair, teh attenuation is set by programming their bias current respectively. But circuit details aren't revealed in the datasheet.

ad605.png
 

jimmykk

Full Member level 2
Joined
Oct 2, 2014
Messages
124
Helped
0
Reputation
0
Reaction score
0
Trophy points
16
Activity points
1,260
OK....I understand that 175 ohm is not the input impedance of the amplifier but what is it then. i am cofused here
 

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
19,738
Helped
4,345
Reputation
8,699
Reaction score
4,305
Trophy points
1,393
Activity points
130,648
Hi,

I understand that 175 ohm is not the input impedance of the amplifier but what is it then.
--> A string of resistors.

Klaus
 
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top