GW Instek GRF-1300A - Manual (Page 100)

GRF-1300A User Manual and Teaching Materials
diagram below.
Up
conversion
Down
conversion
L
ω
c L
ω ω +
L c
ω ω −
We can see from the spectrum shift in the chart above that the
mixing frequency signal is the addition and subtraction of the
input signal and the LO signal. As the frequency mixing dev
generally a non-linear device, it is obvious that a non-linea
combination of frequency distortion and interference will
inevitably occur in the mixing process. The harmonic componen
of the LO signal and the input signal will also be input into t
frequency mixer as well, therefore, the output will hav
ice is
r
ts
he
e the
positive and negative components for each harmonic.
uency
ainly
commonly expressed by the following expansion formula:
In a wireless transceiver circuit, the front-end small-signal low
noise amplifier (LNA) and the IF amplifier (IFA) has far less non-
linear frequency distortion than that produced by the freq
mixer. Therefore the combined non-linear distortion and
frequency interference in the wireless receiver circuit is m
generated by the frequency mixer circuit. The non-linear
characteristics of the frequency mixer for engineering is
2 3
0 1 2 3
... i a a u a u a u = + + + +
In the formula u is the total signal that is added to the input end
of the frequency mixer. Say the composition of u is
3 1 1 2 2 3
cos cos cos u u t u t u t
ω ω ω = + +
98