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Design >> Analog Design >> Basic Curent Conveyor (CCII) operation
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Message started by ssp on Nov 24^th, 2011, 2:42pm

Title: Basic Curent Conveyor (CCII) operation
Post by ssp on Nov 24^th, 2011, 2:42pm

Hi everyone,

I have been bothered by the operation of the following second-generation current conveyor (CCII). In this case it decharges the capacity (arrow points the current direction of the current source). Althought, as I'm new to the integrated circuit world, I have difficulty analysing the behaviour of this circuit, and seeing what's the exact purpose of the OTA amplifier.

Also, what should be the caracteristics of the OTA and why ? (ie. high gain?, large output swing ?..) ?

Thanks for your help,
ssp

Title: Re: Basic Curent Conveyor (CCII) operation
Post by buddypoor on Nov 25^th, 2011, 12:44am

Hi ssp, who has told you that the shown circuit is a CCII ?
That's not true.
A current conveyor has one (non-invertnig) high-resistance and one (inverting) low-resistive input. The last one acts as a current input - contrary to OTA properties. This current is internally "conveyed" to the output and appears there (mostly with a factor of unity) as an output current.

Title: Re: Basic Curent Conveyor (CCII) operation
Post by ssp on Nov 25^th, 2011, 11:21am

Hi buddypoor,

thanks for your response.
Actually, I see the caracteristics of a CCII in that circuit:
Y = non-invertnig, high-resistance
X = invertnig, low-resistance
Z = current input, high resistance

Title: Re: Basic Curent Conveyor (CCII) operation
Post by buddypoor on Nov 25^th, 2011, 11:42am

ssp wrote on Nov 25^th, 2011, 11:21am:

Hi buddypoor,

.............
X = invertnig, low-resistance
...........

But that's not an OTA ! An OTA has two high-impedance inputs !

Title: Re: Basic Curent Conveyor (CCII) operation
Post by ssp on Nov 25^th, 2011, 12:54pm

Right....
but I guess that if the current source injects a very small current, let's say 1 nA, it can fit practically for both the requierements of OTA and the CCII ? This circuit comes from the following article and seems to work until the current source applied is 200 nA:
Narula and al. A time-based VLSI potentiostat for ion current measurements:http://ieeexplore.ieee.org/search/freesrchabstract.jsp?tp=&arnumber=1608062&openedRefinements%3D*%26filter%3DAND%28NOT%284283010803%29%29%26searchField%3DSearch+All%26queryText%3Da+time-based+potentiostat

They don't give the details about the operation of the CCII as they call it.

Title: Re: Basic Curent Conveyor (CCII) operation
Post by buddypoor on Nov 26^th, 2011, 1:08am

My only concern was the shown OTA symbol in connection with the term "CCII". If the shown circuit is able to work or not is another question I did not touch at all.
(By the way: I have no chance to open the IEEE document).

Title: Re: Basic Curent Conveyor (CCII) operation
Post by Vladislav D on Dec 1^st, 2011, 10:36am

This circuit does not make sense. You confuse symbols of voltage and current sources

Title: Re: Basic Curent Conveyor (CCII) operation
Post by loose-electron on Dec 1^st, 2011, 2:18pm

Vladislav D wrote on Dec 1^st, 2011, 10:36am:

This circuit does not make sense. You confuse symbols of voltage and current sources

Agreed - the circuit as drawn needs to be fixed.
Please give a better description of what you are trying to do or trying to understand.

You got a current source with a ground at each end.
Does not compute!
:)

Title: Re: Basic Curent Conveyor (CCII) operation
Post by RobG on Dec 1^st, 2011, 6:56pm

ssp wrote on Nov 25^th, 2011, 12:54pm:

No, the size of the current doesn't matter - the input stages are completely different by definition.