LMX2216 Datasheet, PDF (11/12 Pages) National Semiconductor (TI) – 0.1 GHz to 2.0 GHz Low Noise Amplifier/Mixer for RF Personal Communications

Figures of Merit (Continued)
Due to the presence of image frequencies and the method
in which noise figure is defined noise figures can be mea-
sured and specified in two ways double side band (DSB) or
single side band (SSB) In DSB measurements the image
frequency component of the input noise source is not fil-
tered and contributes to the total output noise at the inter-
mediate frequency In SSB measurements the image fre-
quency is filtered and the output noise is not caused by this
frequency component In most mixer applications where
only one side band is wanted SSB noise figure is 3 dB
higher than DSB noise figure
In this application the LMX2216 is used in a radio receiver
front end where it amplifies the signal from the antenna and
then down converts it to an intermediate frequency The
image filter placed between the LNA and the mixer attenu-
ates the image frequency The mixer is shown to use an LO
signal generated by a PLL synthesizer but depending on
the type of application the LO signal could be generated by
a device as simple as a free-running oscillator The IF output
is then typically filtered by a channel-select filter following
the mixer and this signal can then be demodulated or go
through another down conversion depending upon the in-
termediate frequency and system requirements This exter-
nal filter rejects adjacent channels and also attenuates any
LO feed through Figure 9 shows a cascade analysis of a
typical RF front-end subsystem in which the LMX2216 is
used It includes the bandpass filter and the switch through
which the input RF signal goes in a radio system before
reaching the LNA Typical values are used for the insertion
loss of the various filters in this example
FIGURE 8 Typical Applications Circuit of the LMX2216
TL W 11814 – 18
Comp
1
Filter
2
Switch
3
LNA
4
Filter
5
Mixer
6
Filter
Data per Stage
Gain
N Fig
b2 0
20
b0 6
06
12 3
37
b3 0
30
58
13 7
b3 0
30
OIP3
100 0
100 0
60
100 0
30
100 0
Cumulative Data
Gain
N Fig
IIP3
1
b2 0
20
97 9
2
b2 6
26
96 6
3
97
63
b3 7
4
67
64
b3 7
5
12 5
96
b10 5
6
95
97
b10 5
System Cumulative Values
Gain
N Fig
IIP₃
OIP₃
9 5 dB
9 7 dB
b10 5 dBm
b1 0 dBm
FIGURE 9 Cascade Analysis Example
OIP3
95 9
94 0
60
30
20
b1 0
11