Solid state RF oscillator-detector for flow cytometer

  
Inside:
Repository
A junction field effect transistor (JFET) RF oscillator-detector circuit generates an RF signal for an apparatus for conducting electrical measurements of particles contained in a carrier fluid passing through an aperture in a cytometer flow cell. The JFET oscillator includes a plurality of parallel-coupled JFETs having respectively different VDS
Solid state RF oscillator-detector for flow cytometer - schematic

vs. IDS characteristics, that are biased to operate at square law detection regions of their respective VDS vs. IDS characteristics. One JFET operates in Class C mode, while the other operates in Class AB mode. An RF resonant circuit is electrically coupled to the JFETs and to the measurement cell, and is operative to establish the frequency of an RF field applied to the measurement cell. An RF load change detection circuit is coupled to the RF resonator circuit and is operative to detect an RF load change associated with a modification of the RF field as a result of a particle within the measurement cell aperture. 1. A circuit wherein said RF oscillator-detector comprises a junction field effect transistor (JFET)-based RF oscillator, that includes a plurality of parallel-coupled JFETs having respectively different VDS vs. IDS characteristics, with a first JFET of said plurality of JFETs operating in Class C mode, and a second JFET of said plurality of JFETs operating in Class AB mode. 2. A junction field effect transistor (JFET) RF oscillator-detector circuit for use in an apparatus for conducting electrical measurements of particles contained in a carrier fluid passing through an aperture in a measurement cell to which an electric field is applied, said JFET RF oscillator comprising: a plurality of parallel-coupled JFETs having respectively different VDS vs. IDS characteristics, and being biased to operate at square law detection regions of their respective VDS vs. IDS characteristics, a first JFET of said plurality of JFETs operating in a first class mode, and a second JFET of said plurality of JFETs operating in second class mode different from said first class mode; an RF resonant circuit electrically coupled to said plurality of parallel-coupled JFETs and to said measurement cell, and establishing the frequency of an RF field applied to said measurement cell; and an RF load change detection circuit coupled to said RF resonator circuit and being operative to detect an RF load change associated with a modification of said RF field as a result of a particle within said measurement cell aperture. 3. A JFET RF oscillator-detector circuit according to claim 2, wherein said RF resonant circuit comprises a low Q RF resonant circuit containing a transformer that is operative to step up an RF voltage variation output of said RF oscillator-detector to an elevated RF voltage variation applied to said measurement cell, and increase the electrical impedance of said RF oscillator-detector seen by said measurement cell. 4. A JFET RF oscillator-detector circuit according to claim 3, further including a current mirror coupled to an RF load sensing node of said RF load change detection circuit and being operative to maintain a constant output impedance over changes in compliance voltage. 5. A JFET RF oscillator-detector circuit according to claim 3, wherein said transformer includes a tickler transformer winding coupled to an RF oscillation detector for providing an indication of the operational state of said JFET RF oscillator. 6. A JFET RF oscillator-detector circuit according to claim 4, further including a bypass capacitor coupled to said RF load sensing node, and wherein parameters of said bypass capacitor and said current mirror are selected to maximize the magnitude of an RF pulse at said RF load sensing node. 7. A JFET RF oscillator-detector circuit according to claim 6, wherein said low Q RF resonant circuit includes a glass piston variable tuning capacitor coupled with a winding of said transformer for establishing the reson



Recommended videos


  • Vacuum Tubes (Valves):
     
  • Microwave doppler sensor lamp with perplexingly simple circuitry.
    Duration: 13:30.
  • Nikola Tesla 12-Volt 4-Battery charger circuit impossible? DIY
    Duration: 1:37.

News


.