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.

Register Log in

Multiple current sources charging a cap- getting the wrong result

Status
Not open for further replies.
A

amsdesign

Member level 3
Joined
Aug 26, 2015
Messages
67
Helped
0
Reputation
0
Reaction score
0
Trophy points
6
Activity points
550
Hello everyone,

This is how my circuit looks like


multiple-pfdcp.png


All the current sources are just current mirrors-each 20uA.
When I increase the number of source and sinks, the charging time becomes slower rather than getting faster.

For example. If I set 4 source and sinks. At time t, the output out is 1.02 volts.
If I decrease it to 4 source and sinks, for the same t, the output is now at 1.04 volts.

Can anyone tell me why this is happening? As I increase the current shouldn't the cap charge faster?
 

Hi, if this answer relates to your question: I just read in a webpage about "charge and discharge of a capacitor" that the greater the resistance, the slower a capacitor charges, maybe that with each additional current mirror additional resistance is added, slowing charge time down.
There's a formula to calculate charge and discharge time, this page might be of use:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html

That might clarify what is happening better.
 

d123 said:
Hi, if this answer relates to your question: I just read in a webpage about "charge and discharge of a capacitor" that the greater the resistance, the slower a capacitor charges, maybe that with each additional current mirror additional resistance is added, slowing charge time down.
There's a formula to calculate charge and discharge time, this page might be of use:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html

That might clarify what is happening better.
Click to expand...


Doesn't the charging time constant inversely vary with the product of R and C?
 

I presume, you are reporting simulation results. Wouldn't it be appropriate to analyze the simulation in detail, e.g. look at individual transistor voltages and currents in the transient analysis to find out why the circuit doesn't behave as expected?

You have all the information at your fingertips, he have about nothing.
 

I thought that basically T = RC. So greater R = longer T. Maybe we're talking about different things, anyway, hope you have discovered the cause.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top