Frequency synthesizer for a level measuring device and a level measuring device

• US 8,416,124 B2
• Filed: 07/09/2010
• Issued: 04/09/2013
• Est. Priority Date: 07/10/2009
• Status: Active Grant

• Current Assignee: Krohne Messtechnik GmbH & Co. KG
• Original Assignee: Krohne Messtechnik GmbH & Co. KG
• Inventors: Gerding, Michael
• Primary Examiner(s): Keith, Jack W
• Assistant Examiner(s): BYTHROW, PETER M
• Application Number:
  US12/833,113
• Publication Number:
  US 20110006811A1
• Time in Patent Office: 1,005 Days
• Field of Search: 342/118, 342/124, 342/165, 342/168, 342/175, 342/195, 708/271
• US Class Current: 342/124
• CPC Class Codes: G06F 1/0328 in which the phase increment is adjustable, e.g. by using an adder-accumulator
• CPC Class Codes: H03B 19/00 Generation of oscillations by non-regenerative frequency multiplication or division of a signal from a separate source transference of modulation from one carrier to another H03D7/00
• CPC Class Codes: H03B 21/02 by plural beating, i.e. for frequency synthesis ; Beating in combination with multiplication or division of frequency digital frequency synthesis using a ROM G06F1/02; digital frequency synthesis in general H03K; indirect frequency synthesis using a PLL H03L7/16

Abstract

A frequency synthesizer for a time base generator of a level measuring device which works according to the radar principle, with at least one first output for output of a first frequency signal, with at least one second output for output of a second frequency signal, and with a reference oscillator for producing a reference frequency signal, the first frequency signal and the second frequency signal having a small difference frequency relative to one another, the first frequency signal being producible by interaction of the reference oscillator with a direct digital synthesizer. The first frequency signal and second frequency signal can be generated with especially low noise by the second frequency signal being derived from the reference oscillator without interconnection of a direct digital synthesizer and the direct digital synthesizer being operated such that only a noise spectrum is produced which is at least partially minimized.

Claims

1. Frequency synthesizer for a time base generator of a level measuring device which works according to the radar principle, comprising:

a reference oscillator for producing a reference frequency signal,

a direct digital synthesizer,

at least one first output, and

at least one second output,

wherein the reference oscillator is arranged to interact with the direct digital synthesizer to produce at least one first frequency signal at the at least one first output,

wherein the reference oscillator is arranged to produce a second frequency signal at said at least one second output without interconnection of the direct digital synthesizer, the second frequency signal being only slightly different from the first frequency signal,

wherein the direct digital synthesizer is adapted to produce only an at least partially minimized noise spectrum, and

wherein the direct digital synthesizer is adapted to operate with phase shifts which do not produce noise lines as a result of phase truncation.

2. Frequency synthesizer in accordance with claim 1, wherein a digital/analog converter is encompassed by the direct digital synthesizer is adapted to operate at maximum resolution.

3. Frequency synthesizer in accordance with claim 2, wherein the digital/analog converter which is encompassed by the direct digital synthesizer is adapted to operate at an oversampling frequency.

4. Frequency synthesizer in accordance with claim 1, wherein the direct digital synthesizer comprises an n-bit phase accumulator and a phase storage triggered by the phase accumulator, the phase accumulator being parameterizable with an n-bit shift word, only the m most significant bits (MSBs) of the phase accumulator activating the phase storage, the n-bit shift word at bit position (n-m) having a 1 and all lower bit positions of the shift word having an 0.

5. Frequency synthesizer in accordance with claim 1, wherein the direct digital synthesizer is adapted to operated at a maximum frequency.

6. Frequency synthesizer in accordance with claim 1, further comprising a first frequency divider between the direct digital synthesizer and the first output such that the first output is able to be supplied with the output signal of the first frequency divider.

7. Frequency synthesizer in accordance with claim 6, further comprising a second frequency divider between the reference oscillator and the second output such that the second output is able to be supplied with the output signal of the second frequency divider.

8. Frequency synthesizer in accordance with claim 1, further comprising a first filter between the output of the direct digital synthesizer and a first output of the frequency synthesizer.

9. Frequency synthesizer in accordance with claim 8, wherein the first filter is a bandpass filter, and the output signal of the first filter is received by a first frequency divider.

11. Frequency synthesizer in accordance with claim 1, wherein a mixer is provided between the direct digital synthesizer and the first output, wherein a first input of the mixer connected at least indirectly with the output signal of the direct digital synthesizer, wherein a second input of the mixer is connected at least indirectly with the output signal of the reference oscillator and wherein the first output is connected at least indirectly with the output signal of the mixer.

12. Frequency synthesizer in accordance with claim 11, further comprising a first filter between the output of the direct digital synthesizer and a first output of the frequency synthesizer and a first frequency divider between the direct digital synthesizer and the first output such that the first output is able to be supplied with the output signal of the first frequency divider, wherein a mixer is provided between the output of the first filter and the input of the first frequency divider in a series arrangement of the direct digital synthesizer, first filter, mixer, first frequency divider, and first output.

13. Frequency synthesizer in accordance with claim 12, wherein a second filter is provided between the output of the reference oscillator and the second input of the mixer, the second filter being a bandpass filter.

10. Frequency synthesizer for a time base generator of a level measuring device which works according to the radar principle, comprising:

a reference oscillator for producing a reference frequency signal,

a direct digital synthesizer,

at least one first output,

at least one second output, and

a first filter between the output of the direct digital synthesizer and a first output of the frequency synthesizer, the first filter being a bandpass filter,

wherein the reference oscillator is arranged to interact with the direct digital synthesizer to produce at least one first frequency signal at the at least one first output,

wherein the reference oscillator is arranged to produce a second frequency signal at said at least one second output without interconnection of the direct digital synthesizer, the second frequency signal being only slightly different from the first frequency signal,

wherein the direct digital synthesizer is adapted to operate with phase shifts, the only resulting truncations of which that produce noise lines are those which produce noise lines that are in a blocking region of the bandpass filter and wherein the bandpass filter is connected downstream of the direct digital synthesizer.

14. Level measurement device which operates according to the radar principle, comprising:

a reference oscillator for producing a reference frequency signal,

a direct digital synthesizer,

at least one first output, and

at least one second output,

wherein the reference oscillator is arranged to interact with the direct digital synthesizer to produce at least one sampling frequency signal at the at least one first output,

wherein the reference oscillator is arranged to produce a transmission frequency signal at said at least one second output without interconnection of the direct digital synthesizer, the transmission frequency signal being only slightly different from the sampling frequency signal,

wherein the direct digital synthesizer is adapted to produce only an at least partially minimized noise spectrum, and

wherein the direct digital synthesizer is adapted to operate with phase shifts which do not produce noise lines as a result of phase truncation.

15. Frequency synthesizer in accordance with claim 14, wherein the direct digital synthesizer comprises an n-bit phase accumulator and a phase storage which is triggered by the phase accumulator, and wherein the phase accumulator is able to be parameterized with an n-bit shift word.