US 6,208,215 B1 · VCO and filter controlled by common integrated thermal frequency reference

Abstract

A VCO and filter each include a variable transconductance amplifier as a resistive element. The same control bias current is supplied to the variable transconductance amplifier of both the oscillator and filter. This control bias current may be externally supplied, or may be generated on-chip from a thermal RC network formed from base-emitter junctions of bipolar transistors arrayed in single crystal silicon about a heat source. Application of a clock signal from the VCO to the heat source generates a heat pulse which propagates across the arrayed transistors. The resulting change in temperature produces a change in Vbe of the arrayed transistors. The phase shift between the original clock signal and the changed Vbe is determined solely by the time constant τ of the particular thermal RC network. This time constant is a function of the inherent stable thermal resistance and capacitance of the single crystal silicon, and of the location and relative spacing of the arrayed transistors. The time constant is independent of amplitude, frequency, and duty cycle of the original clock signal. The phase shift between the original clock signal and the time-delayed output of the thermal RC network is determined, and a bias control current corresponding to this phase shift is generated and fed back to the VCO and to the filter. A VCO having constant frequency output, and a filter having a bandwidth tied to the VCO frequency, can thus be self-contained on a chip without the need for an external frequency reference.

Claims33

Dependent claims

An apparatus for producing an output signal having a substantially constant frequency, the apparatus comprising:

a voltage controlled oscillator configured to receive a control bias current signal and to produce a clock signal having a first frequency;
a semiconductor workpiece having a thermal resistance and a thermal capacitance;
a heat source positioned at a first point within the semiconductor workpiece, the heat source configured to receive the clock signal and generate a heat pulse in the semiconductor workpiece;
a thermal network formed within the semiconductor workpiece and having a thermal time constant, the thermal network configured to receive the heat pulse and produce a voltage signal based upon the thermal time constant;
a limiting amplifier configured to receive, amplify, and limit the voltage signal to produce a clipped output voltage;
and
a comparator configured to receive the clock signal and the clipped output voltage and produce the control bias current signal corresponding to a phase difference between the clock signal and the clipped output voltage, wherein the voltage controlled oscillator alters the first frequency of the clock signal in response to the control bias current signal.

4 more elements

An apparatus including a voltage controlled oscillator comprising:

an oscillator input node configured to receive an input voltage signal;
an operational amplifier having a noninverting input node, an inverting input node, and an oscillator output node, the noninverting input node of the operational amplifier configured to receive the input voltage signal from the oscillator input node, and the oscillator output node configured to produce a clock signal;
a positive feedback loop between the oscillator output node and the noninverting input node, the positive feedback loop including a fixed transconductance amplifier configured to receive a bias current;
and
a negative feedback loop between the oscillator output node and the inverting input node, the negative feedback loop including a variable transconductance amplifier and a shunt capacitor, the variable transconductance amplifier configured to receive a control bias current which varies relative to the bias current.

2 more elements

An oscillator circuit comprising:

a semiconductor workpiece having a thermal resistance and a thermal capacitance;
a voltage controlled oscillator formed in the semiconductor workpiece and including,
an oscillator input node configured to receive an input voltage signal,
an operational amplifier having a noninverting input node, an inverting input node, and an oscillator output node, the noninverting input node of the operational amplifier configured to receive the input voltage signal from the oscillator input node, and the oscillator output node configured to produce a clock signal having a first frequency,
a positive feedback loop between the oscillator output node and the noninverting input node, the positive feedback loop including a fixed transconductance amplifier configured to receive a first control bias current, and
a negative feedback loop between the oscillator output node and the inverting input node, the negative feedback loop including a variable transconductance amplifier and a first shunt capacitor, the variable transconductance amplifier configured to receive a second control bias current which varies relative to the first control bias current;
and
a thermal frequency reference including,
a heat source positioned at a first point within the semiconductor workpiece, the heat source configured to receive the clock signal and in response to generate a heat pulse in the semiconductor workpiece,
a thermal network formed within the silicon and having a thermal time constant, the thermal network configured to receive the heat pulse and produce a voltage signal based upon the thermal time constant,
a limiting amplifier configured to receive, amplify, and limit the voltage signal and produce a clipped output voltage, and
a comparator configured to receive the clock signal and the clipped output voltage and produce the second control bias current signal corresponding to a phase difference between the clock signal and the clipped output voltage,
whereby the voltage controlled oscillator alters the first frequency of the clock signal in response to the second control bias current signal emitted by the thermal frequency reference.

10 more elements

Dependencies are inferred from the claim text.

VCO and filter controlled by common integrated thermal frequency reference

Life of this patent

VCO and filter controlled by common integrated thermal frequency reference

Life of this patent

Abstract

Claims33