TSH350 Datasheet, PDF (15/21 Pages) STMicroelectronics – 550 MHz, Low Noise Current Feedback Amplifier

Intermodulation Distortion Product
TSH350
6 Intermodulation Distortion Product
The non-ideal output of the amplifier can be described by the following series:
Vout = C0 + C1Vin + C2V2in + …CnVnin
due to non-linearity in the input-output amplitude transfer, where the input is V_in=Asinωt, C₀ is the DC
component, C₁(V_in) is the fundamental and C_n is the amplitude of the harmonics of the output signal V_out.
A one-frequency (one-tone) input signal contributes to harmonic distortion. A two-tone input signal
contributes to harmonic distortion and to the intermodulation product.
The study of the intermodulation and distortion for a two-tone input signal is the first step in characterizing
the driving capability of multi-tone input signals.
In this case:
Vin = A sin ω_1t + A sin ω_2t
then:
Vout
=
C0
+
C
1⁽
A
sin
ω_1t
+
A
sin
ω₂
t)
+
C2
(A
sin
ω₁
t
+
A
sin
ω₂
t
2
)
…
+
Cn
(
A
sin
ω₁
t
+
A
sin
n
ω_2t)
From this expression, we can extract the distortion terms, and the intermodulation terms form a single
sine wave: second order intermodulation terms IM2 by the frequencies (ω₁-ω₂) and (ω₁+ω₂) with an
amplitude of C2A² and third order intermodulation terms IM3 by the frequencies (2ω₁-ω₂), (2ω₁+ω₂), (−
ω₁+2ω₂) and (ω₁+2ω₂) with an amplitude of (3/4)C3A³.
The measurement of the intermodulation product of the driver is achieved by using the driver as a mixer
by a summing amplifier configuration (see Figure 33). In this way, the non-linearity problem of an external
mixing device is avoided.
Figure 33: Inverting summing amplifier (using evaluation board SO8_S_MULTI)
Vin1
R1
Vin2
R2
Rfb
_
+
Vout
100Ω
R
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