RF/DC GENERATOR FOR QUADRUPOLE MASS ANALYZER

• US 3,735,287 A
• Filed: 05/03/1971
• Issued: 05/22/1973
• Est. Priority Date: 05/03/1971
• Status: Expired due to Term

• Current Assignee: Richard Douglas Lowe
• Original Assignee: Richard Douglas Lowe
• Inventors: Lowe, Richard Douglas
• Primary Examiner(s): Segal, Robert
• Assistant Examiner(s): Grimm, Siegfried H.
• Application Number:
  US05/139,414
• Time in Patent Office: 750 Days
• Field of Search: 331/106,109,114,183,117R 250/41.9DS 321/18
• US Class Current: 331/106
• CPC Class Codes: H01J 49/022 Circuit arrangements, e.g. for generating deviation currents or voltages regulating electric or magnetic variables in general, e.g. current, magnetic field G05F; Components associated with high voltage supply high voltage supply per se H02M
• CPC Class Codes: H01J 49/421 Mass filters, i.e. deviating unwanted ions without trapping
• CPC Class Codes: H03L 5/00 Automatic control of voltage, current, or power

Abstract

The specification discloses an improved radio frequency-direct current (RF/DC) generating circuit for use with a quadrupole mass analyzer. A free-running oscillator is employed to generate the radio frequency signal, the oscillator having diode means in the feedback circuit for limiting the dynamic range over which the oscillator must operate. The output of the oscillator is connected through a coil to the rods of the quadrupole mass analyzer which, in conjunction with the coil function as a tuned circuit, thereby the magnitude of the radio frequency applied to the rods is obtained by Q multiplication. A detector circuit is connected to the output of the coil for producing a feedback signal which is compared with a ramp voltage for driving the output of the oscillator as a function of the control ramp input. The detector output is also fed back to the input of two similar circuits for generating equal magnitude with opposite polarity direct current potentials which magnitude varies as a function of the output of the detector and thereby under control of the input control ramp. Additional diodes are provided in the detector circuit to enable the detector to operate near zero volts.

Claims

1. An improved radio frequency-direct current generating circuit comprising:

output means having frequency selective characteristics;

free-running oscillator means connected to said output means for generating an output signal at a frequency determined by said output means, said oscillator means including first and second transistors connected in push-pull relationship, feedback means connected to said transistors for developing a first control signal, and diode means connected in said feedback means for reducing the magnitude of said first control signal thereby controlling the range of operation of said oscillator;

detector means coupled to said oscillator means for producing a second control signal, said detector including first and second paired diodes for rectifying said oscillator outputs, and further diode means connected between said detector and ground for enabling said detector to operate at close to zero volts;

means for producing a ramp voltage;

comparison means connected to said ramp producing means and to said detector means for producing an output signal having a magnitude representing the difference in magnitude between said ramp and said second control signal;

means connected between said comparison means and said oscillator to control the output of said oscillator as a function of said output signal;

first and second direct current generating means for generating opposite polarity direct current potentials, each of said direct current generating means including potentiometer means for generating a direct current control signal, and second comparison means connected to said potentiometer means and to said detector means for producing a direct current output having a magnitude which varies as a function of said direct current control signal; and

means connected to said second comparison means for applying said direct current outputs to said output means.

2. An electrical circuit for generating an output signal having radio frequency and direct current components said circuit comprising:

free-running oscillator means for generating a radio frequency electrical signal;

output means having frequency selective properties coupled to said oscillator means for receiving said radio frequency signal and for establishing the amplitude of said radio frequency signal by Q-multiplication;

detector means connected between said oscillator means and said output means for producing a feedback signal having an amplitude proportional to the amplitude of said radio frequency signal, said detector means including means to enable said detector to operate at close to zero volts;

a variable amplitude control signal source;

comparison means connected to receive said variable amplitude control signal and said feedback signal for producing an output indication proportional to the difference in amplitude therebetween;

means connected to said comparison means and to said oscillator means for controlling the amplitude of said radio frequency signal as a function of said output indication; and

means connected to said output means for producing opposite polarity controlled amplitude direct current signals for application to said output means;

said free-running oscillator means including resonant circuit means including said output means and inductor means coupled thereto, complementary connected transistor means operating in push-pull mode connected to said inductor means, means connected to said resonant circuit and to saId transistor means for producing a driving signal for said transistors, and diode means connected in said last mentioned means for enabling oscillation at low amplitude driving signals.

3. An improved radio frequency/direct current generating circuit comprising:

frequency selective output means for receiving a radio frequency/direct current signal;

radio frequency signal generating means for producing a radio frequency signal by Q-multiplication including said frequency selective output means active means adtive means for driving said selective means;

means for producing a variable control voltage;

means connected to said control voltage producing means and to said output means for producing a difference signal representing the difference in amplitude between said radio frequency signal and said control voltage;

means responsive to said difference signal for controlling the amplitude of said radio frequency signal as a function of said control voltage; and

direct current signal producing means connected to said output means for supplying direct current signals thereto said direct current producing means including potentiometer means for generating a direct current control signal and comparison means connected to said potentiometer means and to said frequency selective output means for producing a direct current output which varies as a function of said direct current control signal.