Precise Low-Current Source


Posted on Apr 25, 2012

A current source that attains a resolution as low as 10 pA is useful in applications where a precise, low-value


Precise Low-Current Source
Click here to download the full size of the above Circuit.

current is needed. When the circuit forces current into ground, the output remains within 2% of the ideal current over the ±100-nA range. Over the -4- to +3.5-V compliance range, the error that appears is less than 5%. This accuracy results from using an OP8O op amp from Precision Monolithics in the feedback loop. The OP8O has an IB of 200 mA typical. For a given voltage (V^), amp Ul A generates an output voltage so that the current through R5 equals V divided by i5 (10 ). This current causes a voltage drop across R5, which is sensed by the unity-gain differential amp (U1B and U2). That amp"s output is connected to the inverting input of U1A, completing the feedback loop. The noise in the circuit is of particular concern, especially that produced by resistor R5. The circuit is limited to low-frequency and dc applications as a result of its 400-n V/kHz noise. For applications that don"t require the circuit"s 10-pA output, lower values of i5 can be substituted. This will increase the bandwidth.




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    LED Night Lamp
    Panner Waveform Generator
    24VDC-220VDC vehicle carried switching power supply based on inverter circuit
    18 watt power amplifier using tle2141c
    lm1881 video sync for tv and lcd monitor separator
    Amp RC
    rotating flashing 230v lights
    Mini Flasher
    A crystal-controlled oscillator



    Top