TSH112IDT(2002) Ver la hoja de datos (PDF) - STMicroelectronics
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TSH112IDT Datasheet PDF : 19 Pages
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TSH110-TSH111-TSH112-TSH113-TSH114
Intermodulation Distortion
A non-ideal output of the amplifier can be de-
scribed by the following development :
Vout=C0+C1(Vin)+C2(Vin)2+C3(Vin)3+...+Cn(Vin)n
due to a non-linearity in the input-output amplitude
transfert. In
component,
the case of Vin=Asinωt, CO is
C1(Vin) is the fundamental,
the DC
CnAn is
the amplitude of the harmonics.
A one-frequency or one-tone input signal contrib-
utes to a harmonic distortion. A two-tones input
signal contributes to a harmonic distortion and in-
termodulation product.
This intermodulation product or intermodulation
distortion of a two-tones input signal is the first
step of the amplifier study for driving capability in
the case of a multitone signal.
In this case Vin=Asinω1t+Bsinω2t, and :
Vout=
CO+C1(Asinω1t+Bsinω2t)
+
C2(Asinω1t+Bsinω2t)2+C3(Asinω1t+Bsinω2t)3
+
...Cn(Vin)n
Vout=
CO+C1(Asinω1t+Bsinω2t)
+
C2(A2+B2)/2-(C2/2)(A2cos2ω1t+B2cos2ω2t)
+
2C2AB(cos(ω1-ω2)t-cos(ω1+ω2)t)
+
(3C3/4)
(A3sinω1t+B3sinω2t+2A2Bsinω2t+2B2Asinω1t)
+
(C3A3sin3ω1t+B3sin3ω2t)
+
(3C3A2B/2)(sin(2ω1-ω2)t-1/2sin(2ω1+ω2)t)
+
(3C3B2A/2)(sin(−ω1+2ω2)t-1/2sin(ω1+2ω2)t)
+
...Cn(Vin)n
In this expression, we can recognize the second
order intermodulation IM2 by the frequencies
(ω1-ω2) and (ω1+ω2) and the third order intermod-
ulation IM3 by the frequencies (2ω1-ω2), (2ω1+ω2),
(−ω1+2ω2) and (ω1+2ω2).
The following graphs show the IM3 of the amplifier
in two cases as a function of the output amplitude.
The two-tones input signal is achieved by the mul-
tisource generator Marconi 2026. Each tone has
the same amplitude. The measurement is
achieved by the spectrum analyser HP 3585A.
Both instruments are phase locked to enhance
measurement precision.
(fig.30): 3rd Order Intermodulation (180kHz &
280kHz)
AV=+4, Rfb=680Ω, no Cfb, RL=100Ω, Vcc=±6V
-60
-65
-70
-75
-80 740kHz
-85 380kHz
-90
80kHz
-95 640kHz
-100
0
1
2
3
4
5
Output Amplitude (V )
peak
(fig.31): 3rd Order Intermodulation (1MHz &
1.1MHz)
AV=+2, Rfb=680Ω, Cfb=2pF, RL=100Ω, Vcc=±2.5V
-60
-65
-70
-75
3.2MHz
-80
3.1MHz
-85
1.2MHz
-90
900kHz
-95
-100
0.0
0.5
1.0
1.5
2.0
Output Amplitude (V )
peak
13/19
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