Synchronous up-conversion direct digital synthesizer

• US 4,926,130 A
• Filed: 01/19/1988
• Issued: 05/15/1990
• Est. Priority Date: 01/19/1988
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Weaver, Lindsay A.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Duong, Tai V.
• Application Number:
  US07/144,904
• Time in Patent Office: 847 Days
• Field of Search: 326/14, 326/30, 326/15, 326/23, 326/16, 326/27, 326/158, 326/159, 326/160, 326/161, 326/25, 326/36, 307/529, 307/479, 331/37, 331/38, 331/42, 331/43
• US Class Current: 327/105
• 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 method and apparatus for generating high frequency signals, comprising generating a fundamental frequency signal over a predefined tuning range using a direct digital synthesizer with a digital to analog converter operating at a predetermined sampling frequency and mixing the fundamental frequency with a high frequency reference signal in a mixer connected to the converter and a reference source. The reference frequency signal is provided by the reference source at a high frequency which is a multiple of the digital to analog converter sampling frequency and is the difference between a desired high frequency output and the fundamental frequency. Where desired a low pass filter is disposed between the synthesizer and the mixer and a band pass filter is disposed between the mixer and any output elements. A divide by N element can be connected between the reference source and the digital to analog converter to provide a sampling clock signal for the converter. In addition, the reference source can operate at even higher frequencies and a divide by M element is disposed between the reference source and both the divide by N element and the mixer. This allows the reference to be used for additional up conversion mixing with low noise at higher multiples of the converter sampling frequency to achieve higher output frequencies.

Claims

1. An apparatus for generating high frequency signals, comprising:

direct digital synthesizer means for generating a fundamental frequency signal over a predefined tuning range, said synthesizer having a digital to analog converter with a sample clock input and said converter operating at a sampling frequency determined by the frequency of an input sampling frequency signal provided at said sample clock input;

a high frequency reference source providing a reference signal at a frequency of M, an odd integer, times N, an integer, times said sampling frequency;

divide-by-M means connected to said high frequency reference source for, receiving said reference signal, dividing said reference signal in frequency by M and providing a first divided reference signal;

divide-by-N means connected between said divide-by-M means and said converter sample clock input for, receiving said first divided reference signal, dividing said first divided reference signal in frequency and providing a second divided reference signal as said sampling frequency signal;

first mixer means connected to an output of said synthesizer and said divide-by-M means for mixing said fundamental frequency signal and said first divided reference signal so as to generate an intermediate frequency output signal; and

second mixer means connected to an output of said first mixer means and said high frequency reference source for mixing said intermediate frequency output signal and said reference signal so as to generate a desired high frequency signal.

2. The apparatus of claim 1 wherein said reference frequency has a value of about 180 MHz, M has a value of 3, and N has a value of 2.

3. The apparatus of claim 1 wherein M has a value of 3.

4. The apparatus of claim 3 wherein N has a value of 2.

5. A method for generating a high frequency signal, comprising the steps of:

providing a first reference frequency signal having a frequency equal to a difference between a desired high frequency output signal and a fundamental frequency signal, and said first reference signal being at a frequency that is a multiple of M, an odd integer value, times N, an integer value, times a value corresponding to a frequency of a sampling frequency signal;

dividing, in frequency, said first reference frequency signal by M to produce a second reference frequency signal;

dividing, in frequency, said second reference frequency signal by N to produce said sampling frequency signal;

providing said sampling frequency signal to a clock input of a digital to analog converter stage of a direct digital synthesizer;

generating said predetermined fundamental frequency signal using said direct digital synthesizer which has said digital to analog converter stage operating at a sampling frequency of said sampling frequency signal;

mixing said second reference frequency signal with said fundamental frequency signal to produce an intermediate output signal; and

mixing said first reference frequency signal with said intermediate output signal to generate said high frequency signal output signal as an output.

6. The method of claim 5 further comprising the step of low pass filtering said fundamental frequency signal prior to mixing with said second reference frequency signal.

7. The method of claim 5 further comprising the step of bandpass filtering said high frequency output signal.

8. The method of claim 5 wherein M has a value of 3.

9. The method of claim 5 wherein N has a value of 2.

10. The method of claim 8 wherein N has a value of 2.

11. The method of claim 5 wherein said first reference frequency signal is of a frequency of about 180 MHz, and M has a value of about 3.

12. The method of claim 11 wherein N has a value of 2.