TS616 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TS616' PDF : 36 Pages View PDF
TS616
5
Intermodulation distortion product
Intermodulation distortion product
The non-ideal output of the amplifier can be described by the following series, due to a non-
linearity in the input-output amplitude transfer:
Vout
=
C0
+
C1
Vi
n
+
C2
Vi
2
n
+
Cn
Vi
n
n
where the single-tone input is Vin=Asinωt, and C0 is the DC component, C1(Vin) is the
fundamental, Cn is the amplitude of the harmonics of the output signal Vout.
A one-frequency (one-tone) input signal contributes to a harmonic distortion. A two-tone
input signal contributes to a harmonic distortion and an intermodulation product.
This intermodulation product, or rather, the study of the intermodulation distortion of a two-
tone input signal is the first step in characterizing the amplifiers capability for driving multi-
tone signals.
The two-tone input is equal to:
Vin = A sin ω1t + B sin ω2t
giving:
t = C0 + C1(A sin ω1t + B sin ω2t) + C2(A sin ω1t + B sin ω2t)2…+ Cn(A sinω1t + B sin ω2t)n
In this expression, we can extract distortion terms and intermodulation terms from a single
sine
with
wave: second-order intermodulation terms IM2 by the
an amplitude of C2A2 and third-order intermodulation
frequencies (ω1 -
terms IM3 by the
ω2) and (ω1 +ω2)
frequencies
(2ω1 - ω2), (2ω1 +ω2), (−ω1 + 2ω2) and (ω1 +2ω2) with an amplitude of (3/4)C3A3.
We can measure the intermodulation product of the driver by using the driver as a mixer via
a summing amplifier configuration. In doing this, the non-linearity problem of an external
mixing device is avoided.
Figure 45. Non-inverting summing amplifier for intermodulation measurements
1kΩ
Vin1
1:√2
50Ω
100Ω
49.9Ω
1kΩ
49.9Ω
Vin1
50Ω
1:√2
100Ω
+
+Vcc
1/2TS616
_
910Ω
300Ω
300Ω
910Ω
Vout diff.
49.9Ω
Rout1
Rout2
49.9Ω
1kΩ
1kΩ
_
1/2TS616
+
-Vcc
49.9Ω
100Ω
√2:1
50Ω
49.9Ω
17/37
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