US 5,969,577 AGranted

Voltage controlled oscillator less sensitive to fluctuation of threshold of component transistors

AssigneeNEC Corporation

InventorMakoto Kaneko

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Abstract

A voltage controlled oscillator is implemented by odd inverters forming a loop, and a depletion type load transistor, a depletion type frequency control transistor and a depletion type compensating transistor supply driving current to an enhancement type driving transistor in each inverter; the compensating transistor is controlled by a reference voltage generator implemented by a series of resistor and a depletion type load transistor, and fluctuation in a fabrication process equally affects the depletion type transistors; when the depletion transistors increases the driving current, the resistor decreases the reference voltage supplied to the gate electrode of the depletion type compensating transistor, and the depletion type compensating transistor cancels the increment of the driving current so as to make the voltage controlled oscillator less sensitive to the fluctuation of the threshold.

Claims8

Dependent claims

A voltage controlled oscillator comprising

odd logic gates forming a signal propagation loop, each of said odd logic gates including
an input node,
an output node connected to the input node of the next logic gate in said signal propagation loop,
a driving transistor responsive to an input potential level at said input node for producing an output potential level opposite to said input potential levels and introducing a piece of time delay variable in dependence on the amount of driving current supplied to,
a load transistor connected to said driving transistor for constantly supplying a first part of said driving current,
a control transistor connected to said driving transistor and responsive to a control voltage signal for supplying a second part of said driving current variable together with the magnitude of said voltage control signal and
a compensating transistor connected to said driving transistor and responsive to a reference voltage signal for supplying a third part of said driving current compensating a difference between the total of said first part and said second part and a design value, and
a reference voltage generator producing said reference voltage signal and varying the magnitude of said reference voltage signal inversely to the current driving capability of said load transistor and the current driving capability of said control transistor.

5 more elements

Dependencies are inferred from the claim text.