Abstract:
A system for providing voltage and current regulator sources based on a oscillator having variable loop gain is described. Only when the oscillator loop gain is at least the value of one does the oscillator oscillate. The oscillator&#39;s ability to oscillate is controlled by the one or more variable impedance or gain devices. Negative feedback of the voltage or current output level is used to control the loop gain of the oscillator circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The benefits of filing this invention as the following listed Provisional application for patents by Fred Mirow are claimed: 61/191,180; VOLTAGE/CURRENT REGULATOR SYSTEM USING CONSTANT LOOP GAIN. FILING DATE Sep. 6, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to electronic regulator circuits and, more particularly, to voltage and current regulator sources capable of providing an output signal level which is insensitive to temperature variations, radiation, and to variations in the input voltage supplied to the regulator circuit. 
     Stable voltage and current regulators are required to power circuits such as A/D converters, and measurement devices to name only a few. In addition current regulator are useful for controlling motors. 
     Most electronic regulators use a zener or bandgap to develop the reference voltage. These references depend on semiconductor properties that are useful over limited temperature range, and radiation levels. Fred Mirow in U.S. Pat. No. 7,456,700 titled “VARIABLE LOOP GAIN OSCILLATOR SYSTEM” described a technique that maintained the oscillator loop gain at unity to develop a stable voltage reference. 
     Accordingly, one of the objects of the invention is to provide electronic regulators which are insensitive to temperature variations, radiation, and to variations in the input voltage supplied to the regulator circuit. 
     An other objective is to provide voltage and current regulator systems that have high temperature, radiation, and voltage stability due to its reliance on component ratios to set circuit thresholds operating values. 
     It is an additional object of the invention to provide electronic regulator circuits that are less susceptible to process variances by relying on impedance ratios thereby providing a more consistently manufacturable circuit. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present invention meet these and other needs. Embodiments of this invention, use one or more signal level controlled variable impedance or variable gain devices along with other elements to form an oscillator. 
     Oscillators consist of a feedback network section combined with an amplifier section. The feedback network is connected to the input and output of the amplifier so as to provide positive feedback and be capable of oscillating. The amplifier has a phase shift of about 0 degrees and the feedback network supplies the remaining phase shift necessary to make the total phase shift at the frequency of oscillation 0 degrees. If the amplifier is phase inverting having a phase shift of about −180 degrees, than the feedback network would provide the required phase shift amount to have 0 degrees total. This oscillator will only oscillate when the loop gain of the amplifier and feedback network is at least one and the phase shift is zero. There are many well-known phase shift networks that can be used as part of feedback network such as the twin T and the Wien Bridge. In addition well known resonate feedback circuits consisting of inductor capacitor networks may be used. 
     The amplifier section has a high temperature and voltage stability due to its reliance on component ratios to set circuit thresholds operating values. Negative feedback networks can be used in the amplifier section to increase phase and gain stability against the effects of temperature and voltage and to accurately set the amplifier section&#39;s gain. The negative feedback is optimally obtained by using a divider network in which the divider network element&#39;s temperature and voltage characteristics are matched. The effects of temperature on the divider network are then decreased. This also decreases the effects on the amplifier section since the divider network primarily determines the gain of it. 
     The oscillator&#39;s feedback network can also use circuits that depend on the ratio of circuit components, including capacitors, inductors, and resistors, to provide stable gain over temperature. 
     There are many well-known methods for implementing oscillator signal controlled gain varying elements. One method is to use signal controlled variable impedance devices. Some examples for use with a voltage input signal are variable resistors obtained by using a FET with its gate connected to input. An other approach is a variable capacitor type using a reverse biased semiconductor junction such as a diode. As the DC voltage across the diode is varied its capacitance also varies. Also a current input signal can be applied by using as one example a variable inductor obtained by using a core of magnetic material which uses the current through the inductor to vary it&#39;s inductance. In addition the temperature variation of a resistor can be used to control the resistance of the resistor. These resistors are known as Resistance Temperature Detectors (RTD) and also thermistors. 
     Likewise there are many well known methods for obtaining signal controlled variable gain devices. An example of this is transistors. The transistor&#39;s gain is varied by varying its DC operating current level in response to input thus obtaining a signal controlled variable gain device. Also, the inductive coupling (mutual inductance) between inductors may be changed in response to an input signal. 
     The detector output is determined by the oscillator state. When the oscillator is oscillating an AC signal is present and when not oscillating, no AC signal is present. The detector input provides the desired type of output signal to the output control input. When used as part of a linear regulator the detector output signal is proportional to the AC input signal level. When used as part of a switching regulator the detector output signal is high or low depending on whether the oscillator is oscillating or not. 
     The output control uses transistors, or in the case switching regulator transistors, or relays to control the voltage or current output level supplied to the load from the external power source. The level of the detector output signal controls the level of turn on of a device such as a transistor, or the duty cycle of switching elements being transistors, or relays. 
     The output control output is used to control the voltage or current level at the regulator output. This output voltage or current level controls a gain-varying element in the oscillator which is used to control the oscillator&#39;s loop gain. As the output control output level varies the output voltage or current varies causing the loop gain to vary. In linear regulators the detector output control output level is of a value that just maintains oscillation by keeping the loop gain value at or very close to one. Switching regulators have the detector output level go high or low depending on whether the oscillator is oscillating or not. The regulator output signal level therefore remains a substantially constant DC voltage or current output signal level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  shows a block diagram of voltage regulator system  1 ; 
         FIG. 2  shows a block diagram of current regulator system  2 ; 
         FIG. 3  shows a block diagram of oscillator  19 A using resistor gain control of voltage regulator system  1 ; 
         FIG. 4  shows a block diagram of oscillator  20 A using inductor gain control of current regulator system  2 ; 
         FIG. 5  shows a block diagram of switching voltage regulator system  1 A using variable resistors gain control; 
         FIG. 6  shows another block diagram of switching voltage regulator system  1 B using variable resistors gain control; and 
         FIG. 7  shows a block diagram of switching voltage regulator system  1 C using variable capacitor gain control; and 
         FIG. 8  shows a block diagram of linear current regulator system  2 A using variable inductor gain control. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the invention is shown in  FIG. 1 . The voltage regulator system  1  comprising oscillator  19 , voltage control  21 , detector  22  and load resistor  25 . Oscillator  19  receives an gain control input signal on line  23  which is also connected to load resistor  25 . The output of oscillator  19  on line  26  is connected to the detector  22  input. The output signal of detector  22  on line  34  is connected to the control input of output control  21 . Output control  21  has its other input on line  17  connected to the supply voltage and its output connected to line  23 . 
     Detector  22  output level is responsive to the oscillation signal level of oscillator  19  on line  26  and its output on line  34  is used to control the output control  21  output voltage level on line  23 . The voltage level on line  23  controls the loop gain of oscillator  19 . As the voltage level on line  23  increases the loop gain of oscillator  19  is reduced below the value of one causing the oscillation to stop and the detector  22  output signal is reduced to zero turning off output control  21  causing the voltage level on line  23  to become zero. 
     In effect the voltage level on line  23  is applied as negative feedback to maintain a relatively low AC signal level on line  26  which occurs at a loop gain value at or very close to one. This causes the voltage level on line  23  to remain substantially at a value that just maintains oscillation. The output control  21  output voltage level therefore remains substantially a constant DC value. 
     An other embodiment of the invention is shown in  FIG. 2 . The current regulator system  2  comprising oscillator  20 , output control  31 , detector  22 , and load resistor  25 . Load resistor  25  connects the output of output control  31  to line  24 . Oscillator  20  receives to input signal as a current flowing in on line  24  and out on line  29 . The other end of line  29  is connected to ground. The output of oscillator  20  on line  26  is connected to the detector  22  input. The output signal of detector  22  on line  34  is connected to the control input of output control  31 . Output control  31  has its other input on line  17  connected to the supply voltage. 
     Detector  22  output level is responsive to the oscillation signal level of oscillator  20  on line  26  and its output on line  34  is used to control the output control  31  output current level to line  24 . The current level on line  24  controls the loop gain of oscillator  20 . As the current level on line  24  increases the loop gain of oscillator  20  is reduced below the value of one causing the oscillation to stop and the detector  22  output signal is reduced to zero turning off output control  31  causing the current level on line  24  to become zero. 
     In effect the current level flowing on line  24  to line  29  is applied as negative feedback to maintain a relatively low AC signal level on line  26  which occurs at a loop gain value at or very close to one. The current level flowing on line  24  to line  29  is of a value that just maintains oscillation. The output control  31  output current level flowing on line  24  to line  29  therefore remains substantially a constant value. 
       FIG. 3  shows a block diagram of oscillator  19 A which uses variable resistors for gain control. Oscillator  19 A is formed by connecting the output of amplifier  60  on line  26  to feedback network  70  and also to one end of variable resistor  56 . The output of feedback network  70  is connected by line  67  to the non-inverting input of amplifier  60 . The inverting input of amplifier  60  is connected to variable resistor  56  and variable resistor  57 . The other end of variable resistor  57  is connected to ground. Resistor  58  is thermally coupled to variable resistor  57 . Resistor  58  is connected between line  23  and ground. 
     Feedback network  70  is frequency selective and provides a substantially fixed signal gain at a given frequency between the input and output of the amplifier  60  so as to provide positive feedback. The negative feedback network consist of variable resistor  56  and variable resistor  57 . The negative feedback signal gain is controlled by the ratio of variable resistor  56  to variable resistor  57 . Variable resistor  56  and variable resistor  57  have substantially matching temperature coefficients and are at substantially the same ambient temperature level. It is understood that instead of variable resistor  56  being used a fixed value resistor could be used with reduced temperature coefficients matching. 
     The resistance value of variable resistor  57  is controlled by the temperature of resistor  58 . The voltage level of on line  23  causes the temperature of resistor  58  to increase above it&#39;s ambient temperature. As the temperature of resistor  58  increases the resistance of variable resistor  57  changes. In this example the resistance of variable resistor  57  increases with increasing temperature causing the level of negative feedback to increase. Since variable resistor  56  and variable resistor  57  have substantially matching temperature coefficients the effects of ambient temperature change have substantially no effect on the level of negative feedback. If variable resistor  56  and variable resistor  57  resistance values decrease with temperature, resistor  58  would be thermally coupled to variable resistor  56  to increase the level of negative feedback as resistor  58  temperature increased. 
       FIG. 4  shows a block diagram of oscillator  20 A which uses a variable inductor for gain control. Oscillator  20 A is formed by connecting the output of amplifier  60  on line  26  to feedback network  70 A and also to one end of resistor  54 . The output of feedback network  70 A is connected by line  24  to the non-inverting input of amplifier  60 . The inverting input of amplifier  60  is connected to resistor  54  and resistor  55 . The other end of resistor  55  is connected to ground. 
     The negative feedback network consist of resistor  54  and resistor  55 . The negative signal level gain is controlled by the ratio of resistor  54  to resistor  55 . Resistor  54  and resistor  55  have substantially matching temperature coefficients. 
     Feedback network  70 A is formed by connecting one end of inductor  50  to line  26  and the other end to resistor  52 . The other end of resistor  52  is connected to line  24 , variable inductor  51  and to resistor  53 . The other end variable inductor  51  and resistor  53  are connected to line  29  which is also connected to ground. Inductor  50  and variable inductor  51  have substantially matching temperature coefficients. It is understood that instead of using fixed value inductor  50  a variable value inductor could be used with increased temperature coefficients matching. 
     Feedback network  70 A is frequency selective and also provides a variable signal level gain between the input and output of the amplifier  60  so as to provide positive feedback. 
     The variable inductor  51  inductance level is controlled by the level of current flowing on line  24  to line  29 . Variable inductor  51  has a much lower DC impedance level than other components connected to line  24  so that substantially all the DC current on line  24  flow&#39;s through it. The variable inductor  51  magnetic core material “μ” decreases as primary current increases causing it&#39;s inductance level to decrease. As the current flowing on line  24  to line  29  increases the variable inductor  51  inductance level decreases causing the signal gain between lines  26  and  24  to decreases at a given frequency. 
     To provide DC voltage isolation to the oscillator  20 A gain control input variable inductor  51  may be replaced by variable inductance transformer  99  having the same magnetic properties as shown in  FIG. 8 . In this case lines  24  and  29  would be connected to the secondary of the transformer and one end of both the resistor  53  and the primary of the transformer would be connected directly to ground. 
       FIG. 5  shows a block diagram of an other implementation of voltage regulator system  1 , switching voltage regulator system  1 A which uses variable resistors for gain control. Switching voltage regulator system  1 A is formed by connecting the output of amplifier  60  on line  26  to feedback network  70 B, detector  22 A input and also to one end of resistor  54 . The output of feedback network  70 B is connected by line  67  to the non-inverting input of amplifier  60 . The inverting input of amplifier  60  is connected to resistor  54  and resistor  55 . The other end of resistor  55  is connected to ground. Detector  22 A output on line  34  goes to the control input of output control  21 A. Output Control  21 A output to load resistor  25  is on line  23  and receives power from battery  114  through line  17 . 
     The negative feedback network consist of resistor  54  and resistor  55 . The negative signal level gain is controlled by the ratio of resistor  54  to resistor  55 . Resistor  54  and resistor  55  have substantially matching temperature coefficients. 
     Feedback network  70 B is formed by connecting one end of inductor  75  to line  26  and the other end to variable resistor  72 . The other end of variable resistor  72  is connected to line  67 , inductor  74  and to variable resistor  73 . The other end inductor  74  is connected to ground. Line  67  is connected by variable resistor  73  to line  23 . Line  23  is also connected to load resistor  25 , capacitor  110 , and output control  21 A output. The other end of capacitor  110  and load resistor  25  are also connected to ground. 
     Feedback network  70 B is frequency selective and provides a variable signal level gain between the input and output of the amplifier  60  so as to provide positive feedback. Capacitor  110  has a very low impedance compared to variable resistor  73  at the frequency of oscillation so as to have no substantial effect on the oscillator. Inductor  74  has a very low DC resistance compared to variable resistor  73  so that substantial all the DC voltage on line  23  is applied across variable resistor  73 . Inductor  75  and inductor  74  have substantially matching temperature coefficients. Also, variable resistor  72  and variable resistor  73  have substantially matching negative temperature coefficients. 
     The detector  22 A output on line  34  level is high or low depending on whether the oscillator is oscillating or not. For this illustration line  34  is chosen to be low when line  26  has substantially zero AC signal level and be high when the AC signal level is substantially greater than zero. 
     The output control  21 A is formed by connecting one end of relay  113  to line  17  and the other end to diode  112  and inductor  111 . It is understood that relay  113  may be replaced by suitable semiconductor device such as transistors. The other end of diode  112  is connected to ground. The other end of inductor  111  is connected to line  23 . Diode  112  is connected so as to be reverse biased when relay  113  connects line  17  to inductor  111 . When relay  113  disconnects line  17  from inductor  111 , diode  112  permits the current through inductor  111  to continue flowing. Inductor  111  and capacitor  110  have high enough values to reduce the switching voltage ripple on line  23  to the desired value. The duty cycle of relay  113  substantially controls the voltage level on line  23 . The greater the percentage of time relay  113  connects line  17  to inductor  111  the higher will be the voltage level on line  23 . As the voltage level on line  23  increases the resistance level of variable resistor  73  decreases and the oscillator loop gain is decreased. At a certain voltage level the loop gain is reduced enough that oscillation stops and the AC signal level on line  26  becomes substantially zero and relay  113  disconnects line  17  from inductor  111 . The voltage level on line  23  now starts to decrease and when it reaches a certain voltage level the loop gain is increased enough that oscillation again starts and the AC signal level on line  26  becomes substantially greater than zero causing relay  113  to again connect line  17  to inductor  111 . The voltage level on line  23  now starts to increase again resulting in a substantially constant DC voltage level on line  23 . 
       FIG. 6  shows a block diagram of an other implementation of voltage regulator system  1 , Switching voltage regulator system  1 B which uses variable resistors for gain control. Switching voltage regulator system  1 B is formed by connecting the output of amplifier  60  on line  26  to feedback network  70 C, detector  22 A input and also to one end of variable resistor  56 . The output of feedback network  70 B is connected by line  67  to the non-inverting input of amplifier  60 . The inverting input of amplifier  60  is connected to variable resistor  56  and variable resistor  57 . The other end of variable resistor  57  is connected to ground. Resistor  58  is thermally coupled to variable resistor  57 . Resistor  58 , load resistor  25  and capacitor  102  are connected between line  23  and ground. Detector  22 A output on line  34  to the control input of output control  21 A. Output control  21 A output is on line  23  and receives power from battery  114  through line  17 . 
     Feedback network  70 C is frequency selective and provides a substantially fixed signal level gain at a given frequency between the input and output of the amplifier  60  so as to provide positive feedback. The negative feedback network consist of variable resistor  56  and variable resistor  57 . The negative signal level gain is controlled by the ratio of variable resistor  57  to variable resistor  56 . Variable resistor  56  and variable resistor  57  have substantially matching temperature coefficients. 
     The resistance value of variable resistor  57  is controlled by the temperature of resistor  58 . The voltage level on line  23  causes the temperature of resistor  58  to increase above it&#39;s ambient temperature. As the temperature of resistor  58  increases the resistance of variable resistor  57  changes. In this example the resistance of variable resistor  57  increase with temperature causing the level of negative feedback to increase. Since variable resistor  56  and variable resistor  57  have substantially matching temperature coefficients the effect of ambient temperature change has substantially no effect on the level of negative feedback. If variable resistor  56  and variable resistor  57  resistance values decrease with temperature, resistor  58  would be thermally coupled to variable resistor  56  to increase the level of negative feedback as resistor  58  temperature increased. 
     Feedback network  70 C is formed by connecting one end of capacitor  81  to line  26  and the other end to resistor  52 . The other end of resistor  52  is connected to line  67 , capacitor  84  and to resistor  53 . The other end capacitor  84  and resistor  53  are connected to ground. Capacitor  81  and capacitor  84  have substantially matching temperature coefficients. Resistor  52  and resistor  53  also have substantially matching temperature coefficients. 
     Feedback network  70 C is frequency selective and provides a substantially constant signal level gain at a given frequency between the input and output of the amplifier  60  so as to provide positive feedback. 
     The detector  22 A output level on line  34  is high or low depending on whether the oscillator is oscillating or not. For this illustration line  34  is chosen to be low when line  26  has substantially zero AC signal level and be high when the AC signal level is substantially greater than zero. 
     The output control  21 A is formed by connecting one end of relay  113  to line  17  and the other end to diode  112  and inductor  111 . It is understood that relay  113  may be replaced by suitable semiconductor device such as transistors. The other end of diode  112  connected to ground. The other end of inductor  111  is connected to line  23 . Diode  112  is connected so as to be reverse biased when relay  113  connects line  17  to inductor  111 . When relay  113  disconnects line  17  from inductor  111 , diode  112  permits the current through inductor  111  to continue flowing. Inductor  111  and capacitor  102  have high enough values to reduce the switching voltage ripple on line  23  to the desired value. The duty cycle of relay  113  substantially controls the voltage level on line  23 . The greater the percentage of time relay  113  connects line  17  to inductor  111  the higher will be the voltage level on line  23 . As the voltage level on line  23  increases the oscillator loop gain is decreased. At a certain voltage level the loop gain is reduced enough that oscillation stops and the AC signal level on line  26  becomes substantially zero and relay  113  disconnects line  17  from inductor  111 . The voltage level on line  23  now starts to decrease and when it reaches a certain voltage level the loop gain is increased enough that oscillation starts again and the AC signal level on line  26  becomes substantially greater than zero causing relay  113  to connect line  17  to inductor  111 . The voltage level on line  23  now starts to increase again resulting in a substantially constant DC voltage level on line  23 . 
       FIG. 7  shows a block diagram of an other implementation of voltage regulator system  1 , Switching voltage regulator system  1 C which uses variable capacitor for gain control. Switching voltage regulator system  1 C is formed by connecting the output of amplifier  60  on line  26  to feedback network  70 D, detector  22 A input and also to one end of resistor  54 . The output of feedback network  70 D is connected by line  67  to the non-inverting input of amplifier  60 . The inverting input of amplifier  60  is connected to resistor  54  and resistor  55 . The other end of resistor  55  is connected to line  23 . Detector  22 A output on line  34  is connected to the control input of output control  21 A. Output control  21 A output is on line  23  and receives power from battery  114  through line  17 . 
     The negative feedback network consist of resistor  54  and resistor  55 . The negative signal level gain is controlled by the ratio of resistor  55  to resistor  54 . Resistor  54  and resistor  55  have substantially matching temperature coefficients. 
     Feedback network  70 D is formed by connecting one end of variable capacitor  90  to line  26  and the other end to resistor  52 . The other end of resistor  52  is connected to line  67 , variable capacitor  91  and to resistor  53 . The other end variable capacitor  91  is connected to ground. Line  67  is connected by resistor  53  to line  23 . Line  23  is also connected to load resistor  25 , capacitor  110 , and output control  21 A output. The other end of capacitor  110  and load resistor  25  are also connected to ground. 
     Feedback network  70 D is frequency selective and provides a variable signal level gain between the input and output of the amplifier  60  so as to provide positive feedback. The capacitance of variable capacitor  90  and variable capacitor  91  is varied by the voltage level applied to them. Capacitor  110  has a very low impedance compared to resistor  53  at the frequency of oscillation so as to have no substantial effect on the oscillator. Resistor  53  has a very low DC resistance compared to the input of amplifier  60  so that substantial all the DC voltage on line  23  is applied across variable capacitor  91 . Variable capacitor  90  and variable capacitor  91  have substantially matching temperature coefficients. It is understood that instead of using variable capacitor  90  a fixed value capacitor  90  could be used with decreased temperature coefficients matching. 
     The detector  22 A output on line  34  level is high or low depending on whether the oscillator is oscillating or not. For this illustration line  34  is chosen to be low when line  26  has substantially zero AC signal level and be high when the AC signal level is substantially greater than zero. 
     The output control  21 A is formed by connecting one end of relay  113  to line  17  and the other end to diode  112  and inductor  111 . It is understood that relay  113  may be replaced by suitable semiconductor device such as transistors. The other end of diode  112  is connected to ground. The other end of inductor  111  is connected to line  23 . Diode  112  is connected so as to be reverse biased when relay  113  connects line  17  to inductor  111 . When relay  113  disconnects line  17  from inductor  111 , diode  112  permits the current through inductor  111  to continue flowing. Inductor  111  and capacitor  110  have high enough values to reduce the switching voltage ripple on line  23  to the desired value. The duty cycle of relay  113  substantially controls the voltage level on line  23 . The greater the percentage of time relay  113  connects line  17  to inductor  111  the higher will be the voltage level on line  23 . As the voltage level on line  23  increases the capacitance level of variable capacitor  91  increases and the oscillator loop gain is decreased. At a certain voltage level the loop gain is reduced enough that oscillation stops and the AC signal level on line  26  becomes substantially zero and relay  113  disconnects line  17  from inductor  111 . The voltage level on line  23  now starts to decrease and when it reaches a certain voltage level the loop gain is increased enough that oscillation start and the AC signal level on line  26  becomes substantially greater than zero causing relay  113  to again connect line  17  to inductor  111 . The voltage level on line  23  now starts to increase again resulting in a substantially constant DC voltage level on line  23 . 
       FIG. 8  shows a block diagram of an other implementation of current regulator system  2 , linear current regulator system  2 A which uses a variable inductor for gain control. Linear current regulator system  2 A is formed by connecting the output of amplifier  60  on line  26  to feedback network  70 E, detector  22 B input and also to one end of resistor  54 . The output of feedback network  70 E is connected by line  67  to the non-inverting input of amplifier  60 . The inverting input of amplifier  60  is connected to resistor  54  and resistor  55 . The other end of resistor  55  is connected to ground. Detector  22 B output on line  34  goes to the control input of output control  31 A. Output Control  31 A output is connected to feedback network  70 E line  24  and feedback network  70 E line  29  is connected to load resistor  25 . The other end of load resistor  25  is connected to ground. Output Control  31 A receives power from battery  114  through line  17 . 
     The negative feedback network consist of resistor  54  and resistor  55 . The negative signal level gain is controlled by the ratio of resistor  55  to resistor  54 . Resistor  54  and resistor  55  have substantially matching temperature coefficients. 
     Feedback network  70 E is formed by connecting one end of inductor  50  to line  26  and the other end to resistor  52 . The other end of resistor  52  is connected to line  67 , one end of both the resistor  53  and the primary of the variable inductance transformer  99 . The other end of both the resistor  53  and the primary of the variable inductance transformer  99  are connected to ground. The secondary of the variable inductance transformer  99  is connected to lines  24  and  29 . Inductor  50  and variable inductance transformer  99  have substantially matching temperature coefficients. It is understood that inductor  50  and variable inductance transformer  99  may use the same core material. 
     Feedback network  70 E is frequency selective and also provides a variable signal level gain between the input and output of the amplifier  60  so as to provide positive feedback. 
     The variable inductance transformer  99  inductance level between line  67  and ground is controlled by the level of current flowing on line  24  to line  29 . The variable inductance transformer  99  magnetic core material “μ” decreases as current increases causing it&#39;s inductance level to decrease. As the current flowing on line  24  to line  29  increases variable inductance transformer  99  inductance level decreases causing the signal gain to decreases at a given frequency between Feedback network  70 E input line  26  and output line  67 . 
     The detector  22 B output on line  34  is proportional to the AC signal level on line  26 . As the AC signal level on line  26  increases the detector  22 B output on line  34  increases. 
     The output control  31 A is formed by connecting one end of transistor  126  to line  17  and the other end to inductor  125 . The transistor gate is connected to line  34 . As the signal level on line  34  increases transistor  126  turns further on allowing more current to pass through it. The other end of inductor  125  is connected to line  24 . Inductor  125  has a high enough impedance at the frequency of oscillation so as to prevent load  25  and the impedance of output control  21 B from having any substantial effect on the oscillator. 
     In effect the current level flowing on line  24  to line  29  is applied as negative feedback to maintain a relatively low AC signal level on line  26  which occurs at a loop gain value at or very close to one. The current level flowing on line  24  to line  29  is of a value that just maintains oscillation. The output control  31  DC output current level flowing on line  24  to line  29  therefore remains substantially a constant value. 
     Having described embodiments of a new and improved system for producing constant level output signals constructed in accordance with the invention, it is believed obvious that numerous modifications and variations of the invention will be suggested to those skilled in the art in the light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiment of the invention described which are within the full intended scope of the invention as defined by the appended claims.