Radio Frequency Integrated Circuit Design - Webs

238 Radio Frequency Integrated Circuit Design
Table 7.3
Results of the Simulation of the Mixer Circuit
Parameter Value
Gain 13.6 dB
(SSB) NF 12.9 dB
IIP3 8.1 dBm
Voltage 3.3V
Current 12 mA
LO frequency 1.95 GHz
RF 2 GHz
IF 50 MHz
value. The noise figure was also simulated and found to be 12.9 dB. This is
close to what was calculated. Most noise came either from R E or from both
the source and the input-matching resistor. A more refined calculation taking
more noise sources into account would have made the calculation agree much
closer with simulation. To determine the IIP3, the LO was set to be 400 mVpp
at 1.95 GHz, and two RF signals were injected at 2.0 and 2.001 GHz. The
fast Fourier transform (FFT) of the output voltage is plotted in Figure 7.35.
From this figure, using a method identical to that used in the broadband LNA
example in Section 6.8, it can be found that the IIP3 is 8.1 dBm. Thus,
simulations are in good agreement with the calculations.
Example 7.6 Image Reject Mixer
Take the balanced mixer cell designed in the last example and use it to construct
an image reject mixer as shown in Figure 7.22. Place a simple lowpass-highpass
phase shifter in the LO path. Place the second phase shifter in the IF path and
Figure 7.35 FFT of a transient simulation with two input tones used to find the IIP3.