• State TI Thinks Resolved
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 50 views
  • Users 0 members are here
Support feedback
Options
Options
Related

JFE2140: Current noise density

Dimitri
Prodigy 160 points
Part Number: JFE2140
Other Parts Discussed in Thread: JFE150

Tool/software:

JFE2140 and JFE150 are the only JFETs that have datasheets with published current noise density. Can I assume that the published current density is frequency independent? Can you please point to the suitable setup for the frequency dependence measurement of the current noise?  Thank you

  • 0
    TI__Mastermind 24980 points

    Hi Dimitri, 

    The current noise density is frequency dependent but remains flat in the broadband region as shown below. The noise can be measured using the JFE150 or JFE2140 EVMs that I designed. I wrote two app notes that cover the operation of each circuit in detail. 

    EVM's:

    JFE150EVM

    JFE2140EVM

    APP Notes:

    JFE150 Ultra-Low-Noise Pre-Amp

    JFE2140 Ultra-Low-Noise Preamplifier

    For noise measurements on these circuits, it is important to either use a battery or very clean power supply. Filtering the supply line is also recommended. 

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 160 points

    Hi Chris,

    Thank you for your kind reply. The picture you provided shows the input referred voltage noise density. My question is about the current noise density. Current noise density is measured with high value gate resistor, say 10-100 GOhm, later the noise of resistor itself is subtracted from the total measured noise. I expected to see the current noise density which is independent of frequency (e.g. as shown in Figure 5 of https://www.ti.com/lit/an/sboa060/sboa060.pdf), maybe with 1/f component. However I got the current noise density, that increases with frequency. I'm trying to understand what I did wrong.

    Thank you again

    Dimitri. 

  • 0 in reply to Dimitri
    TI__Mastermind 24980 points

    Hi Dimitri, 

    My apologies. I missed the current noise when I read your question. Art Kay is our noise expert. He has written a book on noise as well as several app notes. I work directly with him and will consult with him today on your question. For the mean time here is his latest app note you might find helpful on the Impact of Current Noise in CMOS and JFET Amplifiers. 

    https://www.ti.com/lit/an/sboa570/sboa570.pdf?ts=1757385420542

    I will follow up by the end of today on your question. 

    Best Regards, 
    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 160 points

    Hi Chris,

    Thank you for providing the link to the application note. My setup fully follows paragraph 7 of the app note "Measuring Low Current Noise Levels". As I measure JFET and not op amp, I follow Fig.5-3  Non-inverting Configuration. Resistor value 10-100GΩ, parasitic capacitance around 0.2pF (PTFE substrate), parasitic resistor capacitance around 0.02pF. Should I take distributed-element model of the resistor into account (instead of lumpred-element one)?

    Thank you for your support,

    Dimitri