Unable to get current

[momo36]

hi, i would like to habe current from 3 bit . the first bit 40 microA, second bit 20microA and the last bit 10microA. Attached is my circuit design but i am unable to get the current as required. Any want able to help?

 

[ericgibbs]

hi
I get missing models errors with the asc files.
This image shows that the VOUT label is NOT connected.
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[momo36]

but it can openly fine from mine.

 

[ericgibbs]

hi 36,
I have tried again, downloaded all your files, still cannot get it to open, missing model error.

Look a this image, move the VOUT label on your circuit so it is the same as image, else it is NOT connected.

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[spec]

Hi momo,

What DAC are you using?

If you want to sum currents and produce a corresponding voltage out put (so that you can measure the total current), the usual way is to use a current-summing, virtual-earth amplifier (transimpedance amplifier). The transfer function is Vout = -Iin* R23.

UPDATE: The current inputs to the circuit below are the current outputs from the DACs (should be 3 not 4 as shown).

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[ericgibbs]

hi 36,
I have combined and redrawn your asc file, it now runs for me.
Is the image showing the result you are expecting.?
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[momo36]

hi ericgibbs,

thanks for ur help. i would like to have current where bit 1 40micro second bit 20 micro and third bit 10 micro

 

[ericgibbs]

hi ericgibbs,
thanks for ur help. i would like to have current where bit 1 40micro second bit 20 micro and third bit 10 micro

Hi,
Do you mean like this plot.?
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[momo36]

i mean bit one has current of 40 microA, bit 2 has current of 20 micro A and bit 3 has current of 10 micro ampere

 

[ericgibbs]

thanks for ur help. i would like to have current where bit 1 40micro second bit 20 micro and third bit 10 micro

hi,
You did say 40micro second.
I will look at the problem later.

You may find this option for setting the Bits useful for testing, Set the Bits by using the SW SET = 1 or 0

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[momo36]

sorry. wanted current

 

[ericgibbs]

hi,
Which node/component of the circuit are you wanting to measure the current thru.?

 

[momo36]

i wanted to measure the Iout current for bit 1 bit 2 and bit 3

 

[ericgibbs]

i wanted to measure the Iout current for bit 1 bit 2 and bit 3

hi,
You have 3 identical circuits, as drawn each circuit is able to source a current of ~ 50uA
The only parameter that will change with different Bit patterns is Vout.

Is this a College assignment or an actual circuit you are designing.
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[momo36]

it is actual circuit design

 

[eTech]

Hi

Mouse over each output wire (the cursor will change to a current probe icon), then press ALT-Click.
The measurement will display in the waveform pane.

Or

You can use a voltage source as a current meter. Place it in series with each output wire and set its value to zero.
Then mouse over the voltage source and click. The measurement will display in the waveform pane

I changed the trans time to 10uS. I also dded wire labels to example B for clarity.

See attached.

 

[eTech]

hi
I get missing models errors with the asc files.
This image shows that the VOUT label is NOT connected.
E

Open the Switchable_Current_Source.asc file. Then from the Hierarchy menu, select "Open this sheets symbol".
The symbol will be auto created and placed in the current folder.

 

[ericgibbs]

hi 36,
This is one option to get a 10uA,20uA,40uA current for 3 Bits.
Note I have labelled the Bit's MSB,Bit1,LSB.
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[momo36]

h. thanks. can you foward me the real scematic

 

[momo36]

what is this for ? the purpose and function of it?