Equal duty cycle frequency divider

1. Frequency divider, particularly for radio frequency (RF) applications, wherein the division ratio of said frequency diver can be expressed by an integer divisor, preferably an odd numbered integer divisor, the frequency divider comprising:

an input circuit which receives an input signal as well as a first output signal and generates an intermediate signal, the intermediate signal having at least one main spectral component, whose frequency corresponds to the sum or the difference of the frequencies of said main spectral components of said input signal and said first output signal,

an output circuit, which receives said intermediate signal and generates said first output signal whose main spectral component has a frequency corresponding to the frequency of the main spectral component of said intermediate signal divided by an integer, preferably an even numbered integer, and particularly preferably by 4.

2. Frequency divider according to claim 1 , wherein the duty cycle of said first output signal is in the interval of 40-60%, preferably in the interval of 45-55%, and most preferably in the interval of 48%-52%.

3. Frequency divider according to claim 1 , wherein the difference between the signal level of said main spectral component of said first output signal and the spurious first harmonic of said main spectral component of said first output signal is greater than 6 dB, more preferably greater than 10 dB and most preferably greater than 15 dB.

4. Frequency divider according to claim 1 , wherein said input circuit generates said intermediate signal having at least two spectral components, whose frequencies correspond to the sum and the difference of frequencies of said main spectral components of said input signal and said first output signal, wherein said spectral component of said intermediate signal, whose frequency corresponds to said difference of frequencies, is substantially removed by a filter, preferably high-pass filter before said intermediate signal is fed to said output circuit.

5. Frequency divider according to claim 1 , wherein said input circuit generates said intermediate signal having at least two spectral components, whose frequencies correspond to the sum and the difference of frequencies of said main spectral components of said input signal and said first output signal wherein said spectral component of said intermediate signal, whose frequency corresponds to said sum of frequencies, is substantially removed by a filter, preferably low-pass filter, before said intermediate signal is fed to said output circuit.

6. Frequency divider according to claim 4 , wherein said input circuit is a mixer.

7. Frequency divider according to claim 5 , wherein the overall division ratio is 1:5.

8. Frequency divider according to claim 1 , wherein said input circuit is an exclusive OR-gate (XOR-gate).

9. Frequency divider according to claim 4 , wherein the overall division ratio is 1:3.

10. Frequency divider according to claim 8 , wherein said output circuit is a frequency divider, whose division ratio is preferably selected from a group comprising 1:2, 1:4, 1:8, 1:16, and 1:32.

11. Frequency divider according to claim 8 wherein the overall division ratio is switchable by processing said first output signal by at least one logic gate, preferably by an AND- or OR-gate, before feeding it to said input circuit.

12. Frequency divider according to claim 1 , wherein said output circuit is a frequency divider, which is preferably of the low power type and most preferably performs a division by 4.

13. Frequency divider according to claim 1 , wherein said output circuit is a frequency divider whose division ratio is switchable, wherein the division ratio of said output circuit is preferably selected from a group comprising 1:2, 1:4, 1:8, 1:16and 1:32.

14. Frequency divider according to claim 1 wherein said first output signal is further divided to result in a second output signal, preferably by another frequency divider of the low power type or by another switchable frequency divider, whose division ratio is preferably selected from a group comprising 1:2, 1:4, 1:8, 1:16 and 1:32.

15. Frequency divider according to claim 14 , wherein said additional frequency divider or said additional switchable frequency divider can be powered down when the division resulting in said second output signal is not required.

16. Frequency divider according to claim 14 , wherein an overall output signal of the frequency divider is selectable to be said first output signal or said second output signal, wherein selection is preferably done by a multiplexing circuit.

17. Method for dividing a frequency of a main spectral component of an input signal, particularly an RF signal, wherein the division ratio can be expressed by an integer divisor, preferably an odd numbered integer divisor, the method comprising the following steps:

generating an intermediate signal having at least one main spectral component, whose frequency corresponds to the sum or the difference of the frequencies of the main spectral components of said input signal and a first output signal,

generating said first output signal with a main spectral component having a frequency corresponding to the frequency of the main spectral component of said intermediate signal divided by an integer, preferably an even numbered integer, and particularly preferred by 4.

18. Use of a frequency divider according to claim 1 in a tunable frequency conversion or filtering application, preferably in a phase locked loop of a tunable local oscillator for RF receivers, and most preferably for homodyne RF receivers.