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PSoC™ 5, 3 & 1

ArM_1088156
New Contributor

I want a current source to test one of my trans-impedance amplifiers.

My requirement is to generate a dc current source whose value varies between 0.1 nA to 1 nA, if possible up to 1.5 nA.

I hope I can do it with the IDAC8 module and few resistors with the current division principle.

Though I have a few questions regarding this.

1. I'm not able to generate 0.125 uA with software mode (through a program), even though I can do it in hardware mode. Since the IDAC_SetValue function supports only unsigned integers. Is there any way to generate 0.125 uA current with software. After all, I'll control the current source with the help of a LabView program or through a Windows hyper terminal application.

2. I generated a=1 uA current flowing out of the port pin P 0(6) with the IDAC module. I connected a 100 kohm resistor between the pin P 0(6) and PSoC ground and measured the voltage between the 100 kohm resistor. I sourced 1 uA and measured the voltage and seems to be ok with the calculated value.  But, when the measured value is supposed to be more than 3.3 V (PSoC in 3.3V mode), I repeatedly measure the voltage to be only 3.3 V as maximum value even the supposed measured value to be more than 5 V or so. Why is it so?

Kindly suggest answers.

Regards

Arivalagan

India

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1 Solution
odissey1
Honored Contributor II

ArM,

1. I don't understand the issue. The IDAC_Write(1) should produce 0.125 uA in 32 uA full scale mode.

2.   PSoC current source is a current mirror, which needs some headroom to operate; it can't go closer than ~ 0.7V to a corresponding rail. For example, IDAC source can't go above 4.3-4.4V in source mode (5V VDDA operation).

/odissey1

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3 Replies
odissey1
Honored Contributor II

ArM,

1. I don't understand the issue. The IDAC_Write(1) should produce 0.125 uA in 32 uA full scale mode.

2.   PSoC current source is a current mirror, which needs some headroom to operate; it can't go closer than ~ 0.7V to a corresponding rail. For example, IDAC source can't go above 4.3-4.4V in source mode (5V VDDA operation).

/odissey1

View solution in original post

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odissey1
Honored Contributor II

ArM,

I loaded an IDAC8 on 47k resistor and see 6.1mV, which gives 0.13 uA current flow.

/odissey1

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ArM_1088156
New Contributor

Thanks for the response. I too tried with the same current 0.125 uA through a variety of resistors and got similar results.

I try to take this current (125 nA) as the source and build a current divider and generate currents from 0.1 nA to 1 nA. Then drop them through TIA to check its correctness.

Regards

A M

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