Texas Instruments TRF3705, Руководство пользователя

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P
0_low
P
0_high
P
IM3_low
P
IM3_low
P
IM2
f -f
LO 2
f -f
LO 1
f
LO
f +(f -f )
LO 2 1
f +f
LO 1
f +f
LO 2
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EVM Test Procedure
3.2 Two-Tone OIP3 Test
The output third-order intercept point (OIP3) is a measure of the linearity performance of a nonlinear
device. It is measured by a two-tone test. The following exercise measures OIP3 following all listed steps
in
Section 3.1 .
1. Press Mode → More (1 of 2) → Multitone.
2. Highlight row 11 for frequency offset = 4.5 MHz, press Toggle State, and then press Apply Multitone
to turn on a 4.5-MHz tone. Now, two tones with equal amplitude and frequencies, f
1
= 4.5 and
f
2
= 5.5 MHz, are configured for E4438C.
3. Measure the RF power of both RF tones, P
0
, which must be between
–
1.8 dBm to
–
2.8 dBm.
4. Measure the power, P
IM3
, of the third-order intermodulation product associated with each RF tone. It is
approximately – 66.5 dBm after the cable loss compensation.
5. OIP
3
can be calculated by the equation OIP
3
= P
0
+ (P
0
– P
IM3
)/2. The worst OIP3 associated with
either the low- or the high-frequency tone is selected as the OIP3 of the modulator. The OIP3 at 1 GHz
is approximately
– 29.8 dBm ± 1 dBm. Caution must be taken for accurately measuring the small P
IM3
when the large P
0
is present. It is helpful to reduce the span and RBW settings of the spectrum
analyzer so that the IM3 component is at least 20 dB above the noise floor, as well as by increasing
the RF attenuator setting until P
IM3
is no longer varying with increased RF attenuation setting.
Figure 3. Two-Tone OIP3 Output Spectrum
5 SLWU073 – October 2011 TRF3705EVM Evaluation Module
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