TSH110 datasheet(13/19 Pages) STMICROELECTRONICS

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TSH110-TSH111-TSH112-TSH113-TSH114

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Intermodulation Distortion

A non-ideal output of the amplifier can be de-

scribed by the following development :

Vout=C0+C1(Vin)+C2(Vin)

2+C

3(Vin)

3+...+C

n(Vin)

due to a non-linearity in the input-output amplitude

transfert. In the case of Vin=Asinωt, CO is the DC

component, C1(Vin) is the fundamental, CnA

n 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 :

out=

O+C1(Asinω1t+Bsinω2t)

C2(Asinω1t+Bsinω2t)2+C3(Asinω1t+Bsinω2t)3

...C

n(Vin)

out=

O+C1(Asinω1t+Bsinω2t)

C2(A2+B2)/2-(C2/2)(A2cos2ω1t+B2cos2ω2t)

2AB(cos(ω1-ω2)t-cos(ω1+ω2)t)

(3C

3/4)

(A3sin

1t+B

3sin

2t+2A

2Bsin

2t+2B

2Asin

1t)

3sin3

1t+B

3sin

3ω

2t)

(3C

2B/2)(sin(2

1-ω2)t-1/2sin(2ω1+ω2)t)

(3C3B2A/2)(sin(−ω1+2ω2)t-1/2sin(ω1+2ω2)t)

...C

n(Vin)

In this expression, we can recognize the second

order intermodulation IM2 by the frequencies

(

1-ω2) and (ω1+ω2) and the third order intermod-

ulation IM3 by the frequencies (2

1-ω2), (2ω1+ω2),

(

−ω

1+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

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

(fig.31): 3rd Order Intermodulation (1MHz &

1.1MHz)

AV=+2, Rfb=680Ω, Cfb=2pF, RL=100Ω, Vcc=±2.5V

012345

-100

-95

-90

-85

-80

-75

-70

-65

-60

640kHz

80kHz

380kHz

740kHz

O utput Am plitude (V

peak

)

0.0

0.5

1.0

1.5

2.0

-100

-95

-90

-85

-80

-75

-70

-65

-60

900kHz

1.2MHz

3.1MHz

3.2MHz

Output Amplitude (V

peak

)

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