RF Amplifier and Mixer Measurement
The RF amplifier and mixer have also been measured on the PCB. In the front-end chip, the measurement has been possible thanks to the intermediate pads located in the input of the mixer’s LO. The input and output are available because they are connected to the external SAW and IF filter, respectively. This can be seen in the mixer area of the Figure 4-4.
The packaged RF amplifier and mixer have been measured using the test setups described in Figures 4-19 through 4-22.
Figure 4-19 Test setup for measuring the S11 of the RF amplifier and mixer
Figure 4-20 Test setup for measuring the conversion gain of the RF amplifier and mixer
Figure 4-21 Test setup for measuring the noise figure of the RF amplifier and mixer
Figure 4-22 Test setup for measuring the IIP3 of the RF amplifier and mixer
Figure 4-23 External matching network of the RF amplifier and mixer
Figure 4-23 shows the external matching network employed at the input of the RF amplifier and mixer.
Figure 4-24 presents the input return loss measured with a network analyser (Agilent E5071A), which is below -20dB at the working frequency.
Figure 4-25 presents the gain and the noise figure measured with the spectrum analyser (Agilent E4402B). The gain is 12.9dB and the NF is 6dB for a LO input power of 3dBm.
Figure 4-24 RF amplifier and mixer input return loss
Figure 4-25 Gain and noise figure of the RF amplifier and mixer
Figure 4-26 RF amplifier and mixer gain depending on LO input power
The influence of the LO input power on the conversion gain has also been measured. The conversion gain decreases 0.5dB when the LO input power varies from 3dBm to -8dBm. This variation is represented in Figure 4-26. Therefore, if the power at the PLL were lower than specified, but higher than -8dBm, the performance of the mixer would remain almost constant gainwise.
The measured third-order intermodulation point (IIP3) of -19dBm is shown in Figure 4-27. It has been measured with a two-tone input signal from two signal generators (Agilent E4421B) and the spectrum analyser (Agilent E4402B).
Table 4-2 summarises the results for the RF amplifier and mixer. With the exception of gain and linearity, all the parameters meet specifications.
Figure 4-27 IIP3 of the RF amplifier and mixer
TABLE 4-2 Comparison between the parameters specified for the RF amplifier and mixer and the values estimated and measured in simulation
|
Parameter |
Specifications |
Post-layout |
Measurement |
Unit |
|
Gp |
23 |
18.1 |
12.9 |
dB |
|
NF |
6.2 |
5.6 |
5.4 |
dB |
|
OIP3 |
1.5 |
0.5 |
-6.1 |
dBm |
|
IIP3 |
-21.5 |
-17.6 |
-19 |
dBm |
|
S11 |
<-10 |
-30 |
-27.3 |
dB |
|
Current |
<13 |
5.9 |
4 |
mA |
Nevertheless, gain specification will not be a drawback as system gain will be compensated by a higher gain in the IF amplifier stage.
The slight decrease in linearity will lead to slightly worse performance against to possible interferences. The low level of power consumption is apparent, which is less than three times the value initially specified. Therefore, these results are suitable for the RF front-end. Comparing these results with a state-of-the-art device, it is worthwhile to mention that the RF amplifier and mixer, the measurement of which includes package and ESD protection, presents one of the lowest noise figures and relatively high gain.
