US 5,963,101 A · VCO with local feedback for low power supply noise sensitivity

Abstract

The present invention comprises a voltage controlled oscillator (VCO) circuit having high power supply noise rejection. The circuit of the present invention includes an amplifier having positive, negative, and output terminals. A VCO input is coupled to the positive terminal for receiving a control voltage. A replica circuit is coupled to the negative terminal. A replica source follower transistor is coupled to the output terminal and is also coupled to the replica circuit. The replica source follower transistor transmits a replica current from a power supply to the replica circuit and is controlled by the amplifier. The present invention also includes a first and second VCO cell. The first VCO cell and the second VCO cell are both coupled to the replica circuit and to each other and the second VCO cell includes a VCO output for transmitting a VCO output signal. The first and second source follower transistors are respectively coupled to the first and second VCO cells to provide a respective first and second current from the power supply. The output terminal from the amplifier is coupled to control the replica source follower transistor, the first source follower transistor, and the second source follower transistor. The negative terminal of the amplifier receives feedback from the replica circuit such that the replica current, the first current, and the second current are insensitive to noise on the power supply, and such that the output signal is stable regardless of the noise on the power supply.

Drawings

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Drawings

Claims20

Dependent claims

A voltage controlled oscillator (VCO) circuit, comprising:

an amplifier having a positive terminal, a negative terminal and an output terminal;
a VCO input coupled to said positive terminal for receiving a control voltage;
a replica circuit coupled to said negative terminal;
a replica source follower transistor for transmitting a replica voltage from a power supply to said replica circuit;
a first VCO cell coupled to said replica circuit;
a second VCO cell coupled to said first VCO cell and said replica circuit, said second VCO cell having a VCO output for transmitting a VCO output signal;
a first source follower transistor coupled to said first VCO cell to transmit a first voltage from said power supply to said first VCO cell;
a second source follower transistor coupled to said second VCO cell to transmit a second voltage from said power supply to said second VCO cell, said output terminal coupled to control said replica source follower transistor, said first source follower transistor, and said second source follower transistor, said negative terminal receiving feedback from said replica circuit, wherein said replica circuit adjusts said feedback to compensate for noise on said power supply;
and
a first and second load transistor included in each of said first and second VCO cells, said first and second load transistors coupled to directly receive said VCO input independent of said power supply such that said VCO output signal is insensitive to noise on said power supply.

7 more elements

A voltage controlled oscillator (VCO) circuit, comprising:

an amplifier having a positive terminal, a negative terminal and an output terminal;
a VCO input coupled to said positive terminal for receiving a control voltage;
a replica circuit coupled to said negative terminal;
a replica source follower transistor for transmitting a replica voltage from a power supply to said replica circuit;
a first VCO cell coupled to said replica circuit, said first VCO cell including a first and second load transistor;
a second VCO cell coupled to said first VCO cell and said replica circuit, said second VCO cell having a VCO output for transmitting a VCO output signal, said second VCO cell including a third and fourth load transistor;
a first source follower transistor coupled to said first VCO cell to transmit a first voltage from said power supply to said first VCO cell;
a second source follower transistor coupled to said second VCO cell to transmit a second voltage from said power supply to said second VCO cell;
and
said output terminal of said amplifier is respectively coupled to the gate of said first and said second source follower transistors to increase an impedance of said first and said second source follower transistors, said negative terminal receiving feedback from said replica circuit wherein said replica circuit adjusts said feedback to compensate for noise on said power supply, said VCO input coupled to said positive terminal of said amplifier and to said first and second load transistors and said third and fourth load transistors such that said replica voltage, said first voltage, said second voltage, and said VCO output signal are insensitive to noise on said power supply.

7 more elements

In a voltage controlled oscillator (VCO) circuit including a replica circuit coupled to a plurality of VCO cells, a method of maintaining a stable VCO output signal and rejecting noise on a coupled power supply, the method comprising the steps of:

a) receiving a control voltage at a VCO input coupled to a positive terminal of an amplifier, the amplifier having the positive terminal, a negative terminal and an output terminal;
b) transmitting a replica voltage from a power supply to a replica circuit using a replica source follower transistor, the replica circuit coupled to said negative terminal;
transmitting a VCO output signal from a VCO output, said VCO output included in a second VCO cell, the second VCO cell coupled to a first VCO cell and said replica circuit;
c) transmitting a first voltage from said power supply to said first VCO cell using a first source follower transistor coupled to said first VCO cell;
d) transmitting a second voltage from said power supply to said second VCO cell using a second source follower transistor coupled to said second VCO cell, said output terminal coupled to control said replica source follower transistor, said first source follower transistor, and said second source follower transistor, said negative terminal receiving feedback from said replica circuit,
e) adjusting said feedback to compensate for noise on said power supply using said replica circuit;
and
f) receiving said VCO input independent of said power supply using a first and second load transistor included in each of said first and second VCO cells, said first and second load transistors coupled directly to said VCO input such that said VCO output signal is insensitive to noise on said power supply.

5 more elements

Dependencies are inferred from the claim text.

Description4,654 words

Summary997 words

#The present invention relates to the field voltage controlled oscillators. More particularly, the present invention relates to a voltage controlled oscillator (VCO) having a low sensitivity to noise on its power supply.

#Voltage controlled oscillators (VCOs) are well known and widely used in the electronics industry. Within the digital communications field, VCOs are used in a variety of applications. Such applications include, for example, frequency synthesizers, signal generation (e.g., serial transmission clock recovery), and the like. VCOs are typically designed to perform within a given set of boundary conditions and to perform to a specified standard. Typical conditions include, for example, performance over operating temperature ranges, sensitivity to vibration, output sensitivity to interference, and the like. Typical performance standards include, for example, output signal frequency stability, output signal programmability, and the like.

#A typical prior art VCO generates an oscillating output signal having a specified frequency. The signal can have several different wave forms (e.g., square, saw tooth, triangular, etc.). The frequency of the output is tunable and is a function of an input voltage, an external resistance or capacitance, or the like. The type of application in which the VCO is used dictates its operating conditions and performance requirements. However, as in most VCO applications, it is usually important that the output frequency of the VCO is stable and is a consistent function of the control inputs (e.g., voltage, capacitance, and the like).

Brief description of the drawings12 figures

#The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention:

#FIG. 1 shows a schematic block diagram of a VCO in accordance with one embodiment of the present invention.

#FIG. 2 shows a more detailed block diagram of a VCO in accordance with one embodiment of the present invention.

Detailed description3,414 words

#Reference will now be made in detail to the preferred embodiments of the invention, a voltage controlled oscillator having a low sensitivity to power supply noise, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.

#The present invention provides a solution which solves the power supply noise problems associated with the prior art. The present invention is not adversely affected by low frequency noise in the power supply. In addition, the present invention exhibits higher power supply noise rejection than prior art VCOs. Hence, VCOs in accordance with the present invention are well suited for applications requiring exacting VCO performance. The present invention and its benefits are further described below.

#FIG. 1 shows a schematic block diagram of a VCO 100 in accordance with one embodiment of the present invention. VCO 100 illustrates the general scheme of operation of the present invention. VCO 100 is comprised of a plurality of inverters coupled to form a "chain" where the output of the first inverter is coupled to the input of the second inverter, and so on throughout the chain. Each inverter has a positive and a negative input and a corresponding positive and negative output. The first inverter, e.g., inverter 101 of VCO 100 has its outputs coupled to the inputs of the next inverter, and so on, until the last inverter 120 in the chain is coupled. The plurality of inverters between inverter 101 and 120 are represented by dotted lines. The outputs of the last inverter 120 are coupled to the inputs of the first inverter 101. The resulting feed back effects an oscillation within VCO 100. The number of inverters included in VCO 100 largely determines the resulting natural frequency of oscillation and the total gain. The frequency of oscillation is variable over a range. The degree of variation is determined by the application of a control voltage to the circuitry comprising each inverter. Feedback to the inputs Vi and Vi.sub.n from the outputs Vo and Vo.sub.b sustain the oscillation. The output signal of VCO 100 is typically taken from the outputs Vo and Vob of the last inverter, inverter 120.

Facts

Application

08/972,770Filed 18 Nov 1997

Granted

5 Oct 1999

Term ended

18 Nov 2017

Estimated · how

20 years from earliest known nonprovisional domestic filing. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination. Patent term adjustment is unavailable; no adjustment was added.

Classification3 codes

H03K 3/013
Details: modifications of generator to prevent operation by noise or interference
H03K 3/03
By the use of logic circuits, with internal or external positive feedback: astable circuits
H03K
Pulse technique

VCO with local feedback for low power supply noise sensitivity

Life of this patent

VCO with local feedback for low power supply noise sensitivity

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims20

Description4,654 words

Drawings

Classification3 codes

Life of this patent

Description4,654 words