Constant current r.f. generator
First Claim
1. A voltage source for producing a constant output voltage at radio frequencies in the presence of large voltage standing wave ratios comprising,a field effect transistor having at least a gate and a drain,means for applying a radio frequency signal to said gate,means for applying a voltage to said drain including a transformer having a first winding in series with said drain,said field effect transistor having an output circuit including a second winding of said transformer, andmeans for applying a first d.c. voltage to said first winding remote from said drain to produce operation of said field effect transistor in its saturated region for Class C operation, andmeans for varying the voltage applied to the said first winding remote from said drain to provide a constant amplitude output voltage at the output of said second winding.
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Accused Products
Abstract
The present invention achieves constant voltage at radio frequencies to drive a constant voltage to constant current converter, by employing a tightly coupled d.c. feedback loop to control the voltage via a transformer to the drain of a FET operated as a Class C amplifier in the saturated mode whereby among other advantages, the amplifier can withstand, without damage, very high VSWRs. Control is affected by a high gain differential amplifier which compares a d.c. voltage derived from the r.f. output of the system against a highly stable d.c. voltage reference. A controller, responding to the output of the differential amplifier causes a first level of voltage to be applied to the drain of the FET when the system is not loaded and causes a second voltage varying between said first level and a higher level when the system is loaded. In the lower voltage condition the controller is effectively removed from the system so that it does not have to drop a high voltage to a low voltage; the low voltage being supplied effectively from a separate source.
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Citations
12 Claims
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1. A voltage source for producing a constant output voltage at radio frequencies in the presence of large voltage standing wave ratios comprising,
a field effect transistor having at least a gate and a drain, means for applying a radio frequency signal to said gate, means for applying a voltage to said drain including a transformer having a first winding in series with said drain, said field effect transistor having an output circuit including a second winding of said transformer, and means for applying a first d.c. voltage to said first winding remote from said drain to produce operation of said field effect transistor in its saturated region for Class C operation, and means for varying the voltage applied to the said first winding remote from said drain to provide a constant amplitude output voltage at the output of said second winding.
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9. A voltage source for producing a constant voltage at radio frequencies in the presence of large voltage standing wave ratios, comprising,
a field effect transistor having at least a gate and a drain and having an output circuit including a drain circuit, and means for varying the d.c. voltage applied to said drain circuit to produce a constant amplitude radio frequency voltage at the output of said transistor.
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12. A voltage source for producing a constant amplitude RF output voltage in the presence of large load variations producing large voltage standing wave ratios comprising
a field effect transistor having at least a gate and a drain, means for applying an RF signal to said gate, a d.c. voltage source, a drain circuit including an output circuit and an impedance connected between said voltage source and said drain, means for applying voltage from said d.c. voltage source to said impedance remote from said drain, and means for varying said voltage applied to said impedance as a function of variations of the amplitude of said RF voltage to maintain said RF voltage substantially constant.
Specification