Quadrature baseband input to single ended output

[wccheng]

Dear all,

I have question about the frequency band conversion problem. I hope anyone explain it to me. In the up-conversion mixer, this is a quadrature input and differential output mixer. Then, the differential signal combines and gives out a single output. My problem is arisen.

If a modulated signal with bandwidth=10MHz (0-10MHz signal bandwidth) enters the quadrature up-conversion mixer, what is the output signal like at the single ended output. Does it contain two 10MHz bandwidth at the left hand side of the LO and right hand side of the LO respectively? I mean there are one at 990MHz-1GHz and another one at 1GHz-1.01GHz (assume LO=1GHz). If this is correct, I have a question. As I just give a single tone into the quadrature input of the up-conversion mixer, the single ended output just could see the LO+RF tone and the LO-RF tone will be cancel out. Then, which one is correct?

Thanks,

wccheng

 

[jiripolivka]

The I/Q converters process a signal as a vector. Any "single-ended" device processes a signal as a scalar. I do not think you can combine a vector to get more than a scalar; you would have to use two single-ended channels to do that.
You can compare the situation with the linear and circular polarization of a wave. A circularly-polarized wave behaves as a vector- it rotates through space. To recover the vector, you must use a circularly-polarized antenna. If you only use a linearly-polarized antenna, you still receive the wave but only one half of its power.

 

[tony_lth]

If a modulated signal with bandwidth=10MHz (0-10MHz signal bandwidth) enters the quadrature up-conversion mixer, what is the output signal like at the single ended output. Does it contain two 10MHz bandwidth at the left hand side of the LO and right hand side of the LO respectively? I mean there are one at 990MHz-1GHz and another one at 1GHz-1.01GHz (assume LO=1GHz). If this is correct, I have a question. As I just give a single tone into the quadrature input of the up-conversion mixer, the single ended output just could see the LO+RF tone and the LO-RF tone will be cancel out. Then, which one is correct?

You can conduct math calculation for the final results.
Such as in RF receivers, many have IF1 and IF2 output, then use a hybrid(90 deg), and you can select USB (Upper sideband) or LSB from either of the two output. I think your question is the same thing with that.