Continue to Site

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.

Need a Buffer circuit

Status
Not open for further replies.

hithesh123

Full Member level 6
Joined
Nov 21, 2009
Messages
324
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,298
Location
lax
Activity points
3,548
I need a discrete buffer (not opamp).
I tried Emitter follower. I can't live with the 0.7v drop at the output. I tried JFET buffer. The output resistance is higher than what I want.
The output resistance needs to be less than 100 ohms.

The input to the buffer is coming from a voltage divider(6K).
Any ideas?
 

why not use common base or common gate configuration they are current buffers.
it accept the input signal at a low input resistance and delivers almost equal current at the output.
while common collector can be used as voltage buffer,for connecting a high resistance source to a low resistance load and as the output stage.
 

I need a discrete buffer (not opamp).
I tried Emitter follower. I can't live with the 0.7v drop at the output.

Does this mean that no ac coupling is allowed? Otherwise it would be no problem to use a common collector stage with a dc output of zero volts (and two appropriate supply voltages).
And -as far as FET's are concerned - why is it not possible to achieve an output resistance below 100 ohms?
 

Does this mean that no ac coupling is allowed? Otherwise it would be no problem to use a common collector stage with a dc output of zero volts (and two appropriate supply voltages).
And -as far as FET's are concerned - why is it not possible to achieve an output resistance below 100 ohms?

Can you point me FET buffer to a ckt. I tried earlier today. The input stage of diff rcr is a strange beast - page 3 in AM26LS32 datasheet http://ronja.twibright.com/datasheets/line_receivers_driver/am26ls32a.pdf
 

yeah i was referring a circuit sumthing like that.wee pick the coupling capacitor,keeping in view the range of band width required and lower cuttoff frequency.these coupling capacitor decide the lower frequency response
 

I don't understand your reference to AM26LS32, in my opinion, there's no reasonable prototype of an analog buffer circuit that can be copied from the datsheet.

Your specifications aren't completely clear, I think. Your requesting Ro < 100 ohm and Vos < 0.7 V. How much offset and offset drift is acceptable? How about the signal range? Even a perfectly matched discrete buffer will have some offset and a temperature drift of the same. A npn + pnp follower pair is a very simple circuit with reduced voltage shift. If low gain error is an objective, you would possibly go for a feedback buffer structure. There are many options, you are mainly limited my your power of imagination.

P.S.: Page 3 of the datasheet is showing an input clamping circuit, not a buffer, i think.
 

FvM,

I need something close to an opamp buffer. High input resistance (something like 100K to 1M) and low output resistance.
The problem I have now, is that if I connect the output of voltage divider directly to the line receiver. The line receiver introduces an offset of about 200mV.
I need to eliminate this. The 5K, 1K voltage divider output is connected to diff line rcr. I get an offset at the input of diff rcr.
 

Apparently I still don't understand the application problem. A "line receiver" is a digital circuit in my understanding. Where do you need an analog buffer in this situation?
 

Apparently I still don't understand the application problem. A "line receiver" is a digital circuit in my understanding. Where do you need an analog buffer in this situation?

Well, true. But its getting attenuated by 6x. So 5V becomes 0.8V
That's why I need a buffer.
the 0.8v is not a problem for the line receiver, it's sensitive down to 0.2V.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top