Enhanced transmitter and method for a nuclear magnetic resonance logging tool

Patent metadata

Field	Value
Publication number	US-9405035-B2
Application number	US-201213347008-A
Country	US
Kind code	B2
Filing date	Jan 10, 2012
Priority date	Jan 10, 2012
Publication date	Aug 2, 2016
Grant date	Aug 2, 2016

Abstract

An enhanced radio frequency transmitter suitable for use in a nuclear magnetic resonance logging tool, may employ a power amplifier that comprises two pairs of switching amplifiers and a summation stage. The first pair of switching amplifiers together generate a first pair of pulse sequences having an adjustable phase difference, while the second pair of switching amplifiers generate a second pair of pulse sequences, each pulse sequence in the second pair being provided a fixed phase offset from a respective pulse sequence in the first pair. The summation stage forms a combined signal from the pulse sequences in both said first and second pairs. The fixed phase offset operates to at least partly cancel a higher harmonic of the pulse sequences from the combined signal, thereby reducing energy losses downstream from the transmitter.

First claim

What is claimed is:

1. A power amplifier configured for use with a downhole nuclear magnetic resonance transmitter tool, the power amplifier comprising:
a first pair of switching amplifiers that together generate a first pair of pulse sequences having an adjustable phase difference;
a second pair of switching amplifiers that together generate a second pair of pulse sequences, each pulse sequence in the second pair having a phase offset relative to a phase of a different one of the pulse sequences in the first pair; and
a summation stage that forms a combined signal from the pulse sequences in both said first and second pairs,
wherein said phase offset operates in order to at least partly cancel a higher harmonic of the pulse sequences from the combined signal formed by the summation stage.

2. The power amplifier of claim 1 , wherein the higher harmonic is the 3rd harmonic.

3. The power amplifier of claim 2 , wherein the combined signal formed by the summation stage has the pulse sequences in said second pair subtracted from the pulse sequences in said first pair, and wherein the phase offset corresponding to the second pair of pulse sequences is in the set of values consisting of T(3n±1)/3, wherein T is the period of the pulse sequences and n is an integer.

4. The power amplifier of claim 2 , wherein each of the pulse sequences has a 50% duty cycle, wherein the combined signal has the sum of the pulse signals from said first and second pairs, and wherein the phase offset corresponding to the second pair of pulse sequences is in the set of values consisting of T(6n±1)/6, wherein T is the period of the pulse sequences and n is an integer.

5. The power amplifier of claim 1 , wherein the summation stage also comprises at least one transformer having a secondary winding that responds to said pulse sequences, with the pulse sequences of the first and second pairs being driven on respective transformer primary windings.

6. The power amplifier of claim 1 , further comprising a bandpass filter that attenuates the higher harmonics of the combined signal and passes the first harmonic as an output signal to an antenna interface.

7. The power amplifier of claim 6 , further comprising a control circuit that provides oscillatory signals into the first pair of switching amplifiers, the oscillatory signals having phases symmetrically diverging from a desired signal phase by an amount that provides a desired amplitude at said output signal emerging from the summation stage.

8. The power amplifier of claim 7 , wherein the oscillatory signals, provided by the control circuit, are sinusoidal.

9. A downhole nuclear magnetic resonance logging tool that comprises:
at least one antenna;
an antenna interface that includes a bandpass filter coupled onto at least one antenna in order to provide an output signal to the at least one antenna; and
a transmitter coupled to the antenna interface, the transmitter comprising:
a first pair of switching amplifiers that together generate a first pair of pulse sequences having an adjustable phase difference;
a second pair of switching amplifiers that together generate a second pair of pulse sequences, each pulse sequence in the second pair having a phase offset that is relative to a phase of a different one of the pulse sequences in the first pair; and
a summation stage that forms a combined signal from the pulse sequences in both said first and second pairs of pulse sequences, and providing the combined signal to the bandpass filter, wherein said phase offset operates the summation stage in order to at least partly cancel a higher harmonic originating from the generated pulse sequences from the combined signal formed by the summation stage.

10. The downhole nuclear magnetic resonance logging tool of claim 9 , further comprising a receiver coupled to the antenna interface in order to measure a formation response to said antenna's transmission of the output signal.

11. The downhole nuclear magnetic resonance logging tool of claim 10 , further comprising a signal processor coupled to the receiver in order to derive nuclear magnetic response parameters from the formation response.

12. The downhole nuclear magnetic resonance logging tool of claim 9 , wherein the higher harmonic is the 3rd harmonic.

13. The downhole nuclear magnetic resonance logging tool of claim 12 , wherein the combined signal has the pulse sequences in said second pair subtracted from the pulse sequences in said first pair, and wherein the phase offset of the pulse sequences in the second pair is in the set of values consisting of T(3n±1)/3, wherein T is the period of the pulse sequences and n is an integer.

14. The downhole nuclear magnetic resonance logging tool of claim 12 , wherein each of the pulse sequences has a 50% duty cycle, wherein the combined signal has the sum of the pulse signals from said first and second pairs, and wherein the phase offset of the pulse sequences in the second pair is in the set of values consisting of T(6n±1)/6, wherein T is the period of the pulse sequences and n is an integer.

15. The downhole nuclear magnetic resonance logging tool of claim 9 , wherein the summation stage comprises at least one transformer having a secondary winding that responds to said first and second pair of pulse sequences being driven on respective transformer primary windings.

16. The downhole nuclear magnetic resonance logging tool of claim 9 , wherein the bandpass filter attenuates higher harmonics of the combined signal and passes the first harmonic of the combined signal as an output signal, and wherein the downhole nuclear magnetic resonance logging tool further comprises a control circuit that provides oscillatory signals to the first pair of switching amplifiers with the oscillatory signals having phases differing by an amount that provides a desired amplitude to said generated output signal.

17. The downhole nuclear magnetic resonance logging tool of claim 16 , wherein the control circuit manipulates the phase difference of the first pair of pulse sequences in order to provide a smooth envelope for the generated sinusoidal signal pulses.

18. A downhole nuclear magnetic resonance power amplification method that is used downhole with a nuclear magnetic resonance transmitter tool, the method comprising:
providing, by a signal generator, a first pulse sequence with a predetermined duty cycle;
providing, by the signal generator, a second pulse sequence with an adjustable phase relative to the first pulse sequence;
providing, by the signal generator, third and fourth pulse sequences each having a fixed phase offset from respective ones of the first and second pulse sequences; and
combining, by a summation stage, the pulse sequences in order to generate an amplitude-controlled transmit signal, wherein the phase offset operates in order to at least partly cancel a higher harmonic from the amplitude-controlled transmit signal.

19. The downhole nuclear magnetic resonance power amplification method of claim 18 , wherein the higher harmonic is the 3rd harmonic.

20. The downhole nuclear magnetic resonance power amplification method of claim 19 , wherein the amplitude-controlled transmit signal has the pulse sequences in said second pair subtracted from the pulse sequences in said first pair, and wherein the phase offset is in the set of values consisting of T(3n±1)/3, wherein T is the period of the pulse sequences and n is an integer.

21. The downhole nuclear magnetic resonance power amplification method of clai

Assignees

• Tyshko Alexey
• Halliburton Energy Services Inc

Inventors

• Tyshko Alexey

Classifications

• G01R33/3614

  RF power amplifiers · CPC title

• G01R33/3607

  RF waveform generators, e.g. frequency generators, amplitude-, frequency- or phase modulators or shifters, pulse programmers, digital to analog converters for the RF signal, means for filtering or attenuating of the RF signal · CPC title

• G01V3/32 Primary

  operating with electron or nuclear magnetic resonance · CPC title