METHOD AND APPARATUS FOR HIGHLY ACCURATE HIGHER FREQUENCY SIGNAL GENERATION AND RELATED LEVEL GAUGE

• US 20100066589A1
• Filed: 08/03/2009
• Published: 03/18/2010
• Est. Priority Date: 09/18/2008
• Status: Active Grant

• Current Assignee: Enraf B. V.
• Original Assignee: Enraf B. V.
• Inventors: Sehrier, Ronald C., Sai, Bin
• Granted Patent: US 8,659,472 B2
• Time in Patent Office: Days
• US Class Current: 342/124
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: H03L 2207/10 Indirect frequency synthesis using a frequency multiplier in the phase-locked loop or in the reference signal path
• CPC Class Codes: H03L 2207/12 Indirect frequency synthesis using a mixer in the phase-locked loop
• CPC Class Codes: H03L 7/185 using a mixer in the loop H03L7/187 - H03L7/195 take precedence
• CPC Class Codes: H03L 7/22 using more than one loop

Abstract

An apparatus includes a stable local oscillator, which includes a first control loop. The first control loop includes a first voltage-controlled oscillator configured to generate a first output signal and a first phase-locked loop. The apparatus also includes a frequency up-converter configured to increase a frequency of the first output signal. The apparatus further includes a second control loop configured to receive the up-converted first output signal. The second control loop includes a second voltage-controlled oscillator configured to generate a second output signal and a second phase-locked loop. The second control loop may further include a mixer having a first input coupled to the frequency up-converter, a second input coupled to the second voltage-controlled oscillator, and an output coupled to the second phase-locked loop. A reference frequency source may be configured to generate a signal identifying a reference frequency and to provide that signal to the phase-locked loops.

Claims

1. An apparatus comprising:

a stable local oscillator comprising a first control loop, the first control loop comprising (i) a first voltage-controlled oscillator configured to generate a first output signal and (ii) a first phase-locked loop;

a frequency up-converter configured to increase a frequency of the first output signal; and

a second control loop configured to receive the up-converted first output signal, the second control loop comprising (i) a second voltage-controlled oscillator configured to generate a second output signal and (ii) a second phase-locked loop.

2. The apparatus of claim 1, wherein the second control loop further comprises:

a mixer having a first input coupled to the frequency up-converter, a second input coupled to the second voltage-controlled oscillator, and an output coupled to the second phase-locked loop.

3. The apparatus of claim 2, further comprising:

a buffer coupled between the stable local oscillator and the frequency up-converter; and

a filter coupled between the frequency up-converter and the mixer.

4. The apparatus of claim 2, wherein the second control loop further comprises:

a first amplifier coupled between the mixer and the second phase-locked loop;

a filter coupled to the second phase-locked loop; and

a second amplifier coupled between the filter and the second voltage-controlled oscillator.

5. The apparatus of claim 1, wherein the first control loop further comprises:

a filter coupled to the first phase-locked loop; and

an amplifier coupled between the filter and the first voltage-controlled oscillator.

6. The apparatus of claim 1, further comprising:

a reference frequency source configured to generate a signal identifying a reference frequency and to provide the signal identifying the reference frequency to the first and second phase-locked loops.

7. The apparatus of claim 1, further comprising:

an amplifier configured to receive and amplify the second output signal; and

a variable attenuator configured to receive and attenuate the amplified second output signal.

8. The apparatus of claim 7, wherein the variable attenuator is coupled to an antenna configured to transmit wireless signals based on the attenuated second output signal.

9. The apparatus of claim 7, wherein the variable attenuator is coupled to a mixer configured to mix the attenuated second output signal with signals from one of:

an antenna and a directional coupler.

10. The apparatus of claim 1, wherein the second control loop forms part of a first stage;

and

further comprising a second stage configured to receive the second output signal and generate a higher-frequency third output signal, the second stage comprising a third control loop, the third control loop comprising (i) a third voltage-controlled oscillator configured to generate the third output signal and (ii) a third phase-locked loop.

11. A level gauge comprising:

a sensor configured to transmit wireless signals towards material in a tank and receive wireless signals reflected off the material in the tank; and

a processing system configured to identify a level of the material in the tank based on the wireless signals transmitted towards and reflected off the material in the tank;

wherein the sensor comprises;

a phase-locked loop based stable local oscillator configured to generate a first output signal; and

a phase-locked loop based control loop configured to generate a second output signal based on the first output signal.

12. The level gauge of claim 11, wherein:

the phase-locked loop based stable local oscillator comprises (i) a first voltage-controlled oscillator configured to generate the first output signal and (ii) a first phase-locked loop;

the sensor further comprises a frequency up-converter configured to increase a frequency of the first output signal; and

the phase-locked loop based control loop is configured to receive the up-converted first output signal, the control loop comprising (i) a second voltage-controlled oscillator configured to generate the second output signal and (ii) a second phase-locked loop.

13. The level gauge of claim 12, wherein the phase-locked loop based control loop further comprises:

a mixer having a first input coupled to the frequency up-converter, a second input coupled to the second voltage-controlled oscillator, and an output coupled to the second phase-locked loop.

14. The level gauge of claim 12, wherein the sensor further comprises:

a reference frequency source configured to generate a signal identifying a reference frequency and to provide the signal identifying the reference frequency to the first and second phase-locked loops.

15. The level gauge of claim 11, further comprising:

an amplifier configured to receive and amplify the second output signal; and

a variable attenuator configured to receive and attenuate the amplified second output signal.

16. The level gauge of claim 15, wherein the variable attenuator is coupled to an antenna configured to transmit the wireless signals towards the material in the tank, the transmitted wireless signals based on the attenuated second output signal.

17. The level gauge of claim 15, wherein the variable attenuator is coupled to a mixer configured to mix the attenuated second output signal with signals based on the wireless signals reflected off the material in the tank and received by an antenna.

18. A method comprising:

generating a first signal using a stable local oscillator that comprises a first control loop, the first control loop comprising a first voltage-controlled oscillator and a first phase-locked loop;

increasing a frequency of the first signal to produce an up-converted first signal; and

generating a second signal based on the up-converted first signal using a second control loop, the second control loop comprising a second voltage-controlled oscillator and a second phase-locked loop.

19. The method of claim 18, wherein generating the second signal comprises:

mixing the up-converted first signal with an output of the second voltage-controlled oscillator; and

providing a signal generated by the mixing to the second phase-locked loop.

20. The method of claim 18, further comprising:

amplifying the second signal;

attenuating the amplified second signal; and

at least one of;

transmitting wireless signals based on the attenuated second signal; and

processing received wireless signals using the attenuated second signal.