Quadrature sub-harmonic frequency up-converter
View Patent ↗A method and apparatus for frequency up-converting a baseband signal to radio frequency (RF) in two steps using the two quadrature components of a single local oscillator signal. In a first stage, the baseband signal is split into two parts in quadrature with each other and supplied to a quadrature mixer that mixes the one component of the baseband signal with the I component of a local oscillator signal at frequency F LO and separately mixes the other baseband component with the Q component of the same local oscillator to produce an intermediate frequency signal centered at the local oscillator frequency and comprising two components, namely, an I component and a Q component. In the second stage, the intermediate frequency signal is mixed with both components of the same local oscillator signal in a sub-harmonic mixer-to produce a radio frequency output signal having a frequency component at three times the local oscillator frequency minus the baseband frequency.
1. A method for frequency up-converting a first data signal centered at a first frequency to a second data signal containing the same data as said first data signal and centered at a second frequency higher than said first frequency, said method comprising the steps of:
(1) generating first and second oscillator signals having a third frequency that is about ⅓ of said second frequency, said first oscillator signal being 90° out of phase with said second oscillator signal;
(2) receiving said first data signal;
(3) mixing said first data signal with said first oscillator signal to produce a first component of a third data signal centered at a fourth frequency between said first and second frequencies;
(4) mixing said first data signal with said second oscillator signal to produce a second component of said third data signal centered at said fourth frequency and 90° out of phase with said first component of said third data signal;
(5) combining said first and second components of said third data signal to produce a combined third data signal; and
(6) mixing said combined third data signal with at least one of said first and second oscillator signals in a sub-harmonic mixer to produce said second data signal having said second frequency, said second frequency being a harmonic frequency of said third and fourth frequencies.
2. The method of claim 1 wherein said first data signal comprises a baseband data signal.
3. The method of claim 2 wherein said first data signal is centered at 0 Hz.
4. The method of claim 2 wherein said first data signal is centered at a frequency other than 0 Hz.
5. The method of claim 3 wherein said third frequency is ⅓ said second frequency.
6. The method of claim 4 wherein said third frequency is about ⅓ said second frequency.
7. The method of claim 6 wherein said third frequency is within about 333.3 MHz of ⅓ said second frequency.
8. The method of claim 1 wherein said third data signal at said fourth frequency comprises a harmonic at about said third frequency minus said first frequency.
9. The method of claim 1 further comprising the step of:
(7) amplifying said second data signal.
10. The method of claim 1 further comprising the steps of:
(8) converting said first data signal from the voltage domain to the current domain prior to step (3); and
(9) converting said second data signal from the current domain to the voltage domain after step (6).
11. The method of claim 1 wherein step (6) comprises mixing said combined third data signal with both of said first and second oscillator signals.
12. The method of claim 1 wherein step (6) comprises mixing said combined third data signal with one of said local oscillator signals, wherein said one of said local oscillator signals has a substantially higher amplitude that said combined third data signal.
13. A frequency up-converter for converting a first data signal centered at a first frequency to a second data signal containing the same data as said first data signal and centered at a second frequency higher than said first frequency comprising:
an oscillator generating a quadrature signal at a third frequency that about ⅓ of said second frequency, said quadrature signal having a first component having a first phase and a second component having a second phase 90° out of phase with said first component;
a quadrature mixer comprising first and second mixer components, said first mixer component coupled to mix said first data signal with said first component of said oscillator signal to produce a first component of a third data signal centered at a fourth frequency and said second mixer component coupled to mix said first data signal with said second component of said oscillator signal to produce a second component of said third data signal centered at said fourth frequency;
a combining circuit coupled to combine said first and second components of said third data signal to produce a combined third data signal;
a sub-harmonic mixer coupled to receive said combined third data signal at a first input terminal thereof and coupled to receive at least one of said first and second components of said oscillator signal at at least a second input terminal thereof, said sub-harmonic mixer generating said second data signal having said second frequency being a harmonic frequency of said third and fourth frequencies.
14. The apparatus of claim 13 wherein said first data signal comprises a baseband data signal carried on a radio frequency carrier signal.
15. The apparatus of claim 14 wherein said first data signal is centered at 0 Hz.
16. The apparatus of claim 14 wherein said first data signal is centered at a frequency other than 0 Hz.
17. The apparatus of claim 15 wherein said third frequency is ⅓ said second frequency.
18. The apparatus of claim 16 wherein said third frequency is about ⅓ said second frequency.
19. The apparatus of claim 18 wherein said third frequency is within about 333.3 MHz of ⅓ said second frequency.
20. The apparatus of claim 13 wherein said third data signal at said fourth frequency comprises a harmonic at said third frequency minus said first frequency.
21. The apparatus of claim 13 further comprising:
an amplifier coupled to amplify said second data signal.
22. The apparatus of claim 13 further comprising:
(6) a voltage to current converter coupled between said first data signal and said quadrature mixer; and
(7) a current to voltage converter having an input terminal coupled to receive said second data signal and an output terminal.