# US 9,520,861 B1 · System and method for harmonic suppression

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- Number: US 9,520,861 B1
- Document ID: US9520861B1
- Status: Granted
- Kind: B1
- Application number: 14/971,465
- Filed: 2015-12-16
- Granted: 2016-12-13
- Earliest claimed: 2015-12-16
- Assignees: Texas Instruments Incorporated
- Applicants: Texas Instruments Incorporated
- Inventors: Michael A. Wu; Sudipto Chakraborty
- Web page: https://patentgrep.com/patent/US9520861B1

## CPC

- H03K 3/0315: {Ring oscillators}
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)

## Abstract

A system to generate an oscillator signal. The system includes a multi-stage oscillator, where each stage generates an output. The system also includes a first weighting circuit coupled to the multi-stage oscillator. The first weighting circuit taps the outputs of at least some of the stages and applies a first variable weighting factor to each output of the tapped stages to generate a first weighted output for each of the tapped stages. The system also includes a first summing circuit coupled to the first weighting circuit. The first summing circuit sums the first weighted outputs of the tapped stages to produce the oscillator signal.

## Claims

### Claim 1

A system to generate an oscillator signal, comprising:
a multi-stage oscillator, wherein each stage generates an output;
a first weighting circuit coupled to the multi-stage oscillator and configured to:
tap the outputs of at least some of the stages; and
apply a first set of variable weighting factors to the outputs of the tapped stages to generate first weighted outputs for the tapped stages, the weighting factor applied to at least one of the outputs differing from the weighting factor applied to at least one other of the outputs; and
a first summing circuit coupled to the first weighting circuit and configured to sum the first weighted outputs of the tapped stages to produce the oscillator signal.

### Claim 2 (depends on 1)

The system of claim 1 wherein the multi-stage oscillator comprises a voltage-controlled oscillator.

### Claim 3 (depends on 1)

The system of claim 1 wherein the multi-stage oscillator comprises a ring oscillator.

### Claim 4 (depends on 1)

The system of claim 1 wherein the first weighting circuit is configured to tap the output of all of the stages of the multi-stage oscillator.

### Claim 5 (depends on 1)

The system of claim 1 wherein the first set of variable weighting factors is applied such that the resultant sum of the first weighted outputs is near-sinusoidal.

### Claim 6 (depends on 1)

The system of claim 1 wherein each of the first variable weighting factors (an) is determined by:
an=cos(nπ/m)−cos((n+1)π/m),
where n is a tap number and m is a number of stages of the multi-stage oscillator.

### Claim 7 (depends on 1)

The system of claim 1 wherein a number of stages of the multi-stage oscillator is odd.

### Claim 8 (depends on 1)

The system of claim 1 further comprising:
a second weighting circuit coupled to the multi-stage oscillator and configured to:
tap the outputs of the at least some of the stages; and
apply a second set of variable weighting factors to the outputs of the tapped stages to generate second weighted outputs for the tapped stages; and
a second summing circuit coupled to the second weighting circuit and configured to sum the second weighted outputs of the tapped stages to produce a second oscillator signal;
wherein the second oscillator signal comprises a quadrature component of the oscillator signal.

### Claim 9 (depends on 8)

The system of claim 8 wherein the second variable weighting factor is applied such that the resultant sum of the second weighted outputs is near-sinusoidal and shifted 90 degrees from the oscillator signal.

### Claim 10 (depends on 8)

The system of claim 8 wherein:
the variable weighting factors of the first weighting circuit (an) are determined by:
an=cos(nπ/m)−cos((n+1)π/m), and
the variable weighting factors of the second weighting circuit (bn) are determined by:
bn=sin(nπ/m)−sin((n+1)π/m),
where n is a tap number and m is a number of stages of the multi-stage oscillator.

### Claim 11 (depends on 8)

The system of claim 8 wherein the first and second sets of variable weighting factors are determined such that a set of resulting coefficients comprising the first set of weighting factors is equal to a set of resulting coefficients comprising the second set of weighting factors.

### Claim 12

A method for generating an oscillator signal, comprising:
tapping outputs of at least some stages of a multi-stage oscillator;
applying a first set of variable weighting factor to the tapped stages to generate first weighted outputs for the tapped stages; and
summing the first weighted outputs of the tapped stages to produce the oscillator signal.

### Claim 13 (depends on 12)

The method of claim 12 further comprising tapping the output of all of the stages of the multi-stage oscillator.

### Claim 14 (depends on 12)

The method of claim 12 wherein the first set of variable weighting factor is applied such that the resultant sum of the first weighted outputs is near-sinusoidal.

### Claim 15 (depends on 12)

The method of claim 12 wherein the first set of variable weighting factors (an) is determined by:
an=cos(nπ/m)−cos((n+1)π/m),
where n is a tap number and m is a number of stages of the multi-stage oscillator.

### Claim 16 (depends on 12)

The method of claim 12 further comprising:
applying a second set of variable weighting factors to the output of the tapped stages to generate second weighted outputs for the tapped stages; and
summing the second weighted outputs of the tapped stages to produce a second oscillator signal;
wherein the second oscillator signal comprises a quadrature component of the oscillator signal.

### Claim 17 (depends on 16)

The method of claim 16 wherein the second set of variable weighting factors is applied such that the resultant sum of the second weighted outputs is near-sinusoidal and shifted 90 degrees from the oscillator signal.

### Claim 18 (depends on 16)

The method of claim 16 wherein:
the first set of variable weighting factors (an) is determined by:
an=cos(nπ/m)−cos((n+1)π/m), and
the second set of variable weighting factors (bn) is determined by:
bn=sin(nπ/m)−sin((n+1)π/m),
where n is a tap number and m is a number of stages of the multi-stage oscillator.

### Claim 19 (depends on 16)

The method of claim 16 wherein the first and second sets of variable weighting factors are determined such that a set of resulting coefficients comprising the first set of weighting factors is equal to a set of resulting coefficients comprising the second set of weighting factors.

### Claim 20 (depends on 12)

The method of claim 12 wherein the multi-stage oscillator comprises a ring oscillator.