Loading ...
Sorry, an error occurred while loading the content.

Re: Dual Transistors for Active Negative Inductors

Expand Messages
  • Roberto GIUSTO
    I have just created a LTSpice simulation using two 2N2222 transistorsLet me know your comments and suggestions Warmest ciao !                      
    Message 1 of 19 , Oct 25, 2012
    I have just created a LTSpice simulation using two 2N2222 transistors
    Let me know your comments and suggestions

    Warmest ciao !

                              Rob
  • Roberto GIUSTO
    Dear Chris, the series-resistor of 100 Ohm gives Collector currents of 60 mA, therefore, leaving the supply voltage at 7 V and increasing the series-resistor
    Message 2 of 19 , Oct 25, 2012
    Dear Chris,
    the series-resistor of 100 Ohm gives Collector currents of 60 mA, therefore, leaving the supply voltage at 7 V and increasing the series-resistor on the collector up to 470 Ohm, we get 13 mA  (see the enclosed simulation results of DRAFT2)

    Regarding the Source resistance of 5 Ohm, I have replaced the former small-signal Current source (Itest1) with a small-signal Voltage source V2 in series with the required 5 Ohm resistance. The result is here enclosed in DRAFT3.

    It seems this circuit shows "ideal inductive" behaviour at lower frequencies under 10 MHz, ...and "non-Foster" behaviour in the band 30MHz-50MHz..isn't it ?

    Warmest regards,
                        Roberto

    --- Ven 26/10/12, Chris Trask <christrask@...> ha scritto:

    Da: Chris Trask <christrask@...>
    Oggetto: Re: [loopantennas] Re: Dual Transistors for Active Negative Inductors
    A: loopantennas@yahoogroups.com
    Data: Venerdì 26 ottobre 2012, 00:25

     

    >
    > I have just created a LTSpice simulation using two 2N2222 transistorsLet
    me
    > know your comments and suggestions
    >

    What bias voltage and current are you using?

    Looks like the solid line is signal current and the dashed line is
    phase.

    If you place a 5-ohm resistor in series with the signal source you
    should see better results. My simulations showed this impedance
    to be close to ideal.

    Chris

  • Roberto
    Dear Chris, I ve built the circuit using two 2N3904, it s oscillating! Thus, back to my LTSpice simulation now for checking transient behaviour (that is in
    Message 3 of 19 , Nov 25, 2012
    • 0 Attachment
      Dear Chris,
      I've built the circuit using two 2N3904, it's oscillating!

      Thus, back to my LTSpice simulation now for checking transient behaviour (that is in time_domain for large signal) I found that instability affects such circuit configuration.

      Therefore, if you simulate the behaviour in the frequency domain you get just small-signal response of the circuit and you cannot see this instability.

      Look at my simulation result NIC_2N3904_INSTABILITY.pdf in the "Files" section, folder : LTspice_simulates_2-NPN_Neg_INDUCTANCE

      I will send this result also by email, for your convenience...

      Warmest ciao !




      --- In loopantennas@yahoogroups.com, "Chris Trask" <christrask@...> wrote:
      >
      > >
      > > Ciao !
      > > I would try to build a breadboard of "small antenna" @ 27 MHz and I
      > would
      > > like to undertake two different options for active matching, to be
      > compared as
      > > follows :
      > >
      > > Option a) using MAX2180 (AM section) antenna amplifier
      > >
      > > Option b) using BFM505 for practical NIC circuits shown by Chris:
      > > Fig.5 on pag.5 of "Active Negative Inductor" Report
      > > http://home.earthlink.net/~christrask/Active%20Negative%20Inductors.pdf
      > > Fig.6 on pag.5 of "Linvill feedback amplifier" Report
      > > http://home.earthlink.net/~christrask/Linvill%20Feedback%20Amplifier.pdf
      > >
      > > I would be truly glad of receiving your advise
      > >
      >
      > I have done a considerable amount of modeling to determine where the
      > active negative inductors I described would work best. The usable bandwidth
      > of the circuit of Fig. 5 is directly proportional to the embedding
      > impedance. In other words, the usable bandwidth increases as the embedding
      > impedance increases. There is a limit to this imposed by the transistors,
      > and I found the for HF frequencies an embedding impedance of about 5 ohms
      > works best.
      >
      > The combination I would recommend would be to use the negative inductor
      > circuit in a balanced configuration, coupled in place of the varactors in
      > Fig. 4 of my earlier paper on varactor-tuned loop matching networks:
      >
      > http://www.home.earthlink.net/~christrask/Paper011.html
      >
      > To make a balanced negative inductor for this application, add a third
      > winding to transformer T2 of Fig. 5, using a trifilar twist of wires to
      > ensure good coupling and balance. Be careful to get the correct phase
      > connections when doing this. It might be prudent for me to add this
      > application to the negative inductor paper as that was the intended use from
      > the beginning.
      >
      > Chris
      >
    • Chris Trask
      ... This may be due to mismatch of the transistors. If the emitter resistance of the second device is larger than that of the first device you ll end up with
      Message 4 of 19 , Nov 25, 2012
      • 0 Attachment
        >
        >Dear Chris,
        > I've built the circuit using two 2N3904, it's oscillating!
        >
        > Thus, back to my LTSpice simulation now for checking transient behaviour
        > (that is in time_domain for large signal) I found that instability affects
        > such circuit configuration.
        >
        > Therefore, if you simulate the behaviour in the frequency domain you get
        > just small-signal response of the circuit and you cannot see this instability.
        >
        > Look at my simulation result NIC_2N3904_INSTABILITY.pdf in the "Files"
        > section, folder : LTspice_simulates_2-NPN_Neg_INDUCTANCE
        >
        > I will send this result also by email, for your convenience...
        >

        This may be due to mismatch of the transistors. If the emitter resistance of the second device is larger than that of the first device you'll end up with a negative input resistance. Try adding a small resistance in series with the emitter of the first device.

        Chris
      • Roberto GIUSTO
        Dear Chris,                 the circuit is oscillating even using its SPICE model (for transient simulation), actually in these simulations the two
        Message 5 of 19 , Nov 25, 2012
        • 0 Attachment
          Dear Chris,
                           the circuit is oscillating even using its SPICE model (for transient simulation), actually in these simulations the two transistors are identical.

             Looking forward receiving your comments and suggestions
                Warmest regards,
                                             Roberto 

          --- Dom 25/11/12, Chris Trask <christrask@...> ha scritto:

          Da: Chris Trask <christrask@...>
          Oggetto: Re: [loopantennas] Re: Dual Transistors for Active Negative Inductors
          A: loopantennas@yahoogroups.com, loopantennas@yahoogroups.com
          Data: Domenica 25 novembre 2012, 14:51

           


          >
          >Dear Chris,
          > I've built the circuit using two 2N3904, it's oscillating!
          >
          > Thus, back to my LTSpice simulation now for checking transient behaviour
          > (that is in time_domain for large signal) I found that instability affects
          > such circuit configuration.
          >
          > Therefore, if you simulate the behaviour in the frequency domain you get
          > just small-signal response of the circuit and you cannot see this instability.
          >
          > Look at my simulation result NIC_2N3904_INSTABILITY.pdf in the "Files"
          > section, folder : LTspice_simulates_2-NPN_Neg_INDUCTANCE
          >
          > I will send this result also by email, for your convenience...
          >

          This may be due to mismatch of the transistors. If the emitter resistance of the second device is larger than that of the first device you'll end up with a negative input resistance. Try adding a small resistance in series with the emitter of the first device.

          Chris

        • Chris Trask
          ... What is the frequency of the oscillation? My simulation shows that there is a moderate potential for instability around 40MHz or so using the 2N3904. The
          Message 6 of 19 , Nov 25, 2012
          • 0 Attachment
            >
            >Dear Chris,                 
            >the circuit is oscillating even using its SPICE model (for transient
            >simulation), actually in these simulations the two transistors are
            >identical.
            >   Looking forward receiving your comments and suggestions     
            >

            What is the frequency of the oscillation? My simulation shows that there is a moderate potential for instability around 40MHz or so using the 2N3904. The solution to this is to place a resistor in parallel with the reference inductor.


            Chris Trask
            N7ZWY / WDX3HLB
            Senior Member IEEE
            http://www.home.earthlink.net/~christrask/
          Your message has been successfully submitted and would be delivered to recipients shortly.