TEA2029 データシートの表示（PDF） - STMicroelectronics

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TEA2029

APPLICATION NOTE

STMicroelectronics 

TEA2028 - TEA2029 APPLICATION NOTE

Thus, a variable (24o to + 135o) phase lead with a

gain higher than 10dB, must be implemented on-

chip so as to enable the system to enter into

oscillation.

The frequencydead points correspond to the maxi-

mum internal phase variations. This phase shift is

controlled by voltage V22 whose value of 5.6V ± 0.7

is determined by two diodes.

From the Figure 21, the non-linearity of phase-fre-

quency characteristics is clearly apparent. If linear

voltage-frequency response is required for a sym-

metrical gain of φ1 loop, it would then be necessary

to implement a non-linearity, on the phase control

amplifier A4, but in the opposite direction.

D. - STUDY OF THE INTERNAL AMPLIFIER

Let’s study the gain and phase response of

V18

VIN

as

a function of V22.

V22

=

VC

K

where

K

is

a

non-linear

coefficient

To start with, the ”VC” voltage of comparator ”A3”

is taken as reference parameter.

The dynamic representation of the output stage

can be depicted as below (Figure 22).

with

:

I2’

=

1

+

i2

jω R1

C1

(at

f

=

500kHz)

R1

C1

ω

=

1

⇒

i2’

=

i2

1+

j

and

Z

=

R1

+

1

jω C

<<

R

⇔

i

≈

i2’

R1C1 network produces -45o phase lag of ”i” with

respect to ”i2”, around 500kHz.

V18 ≈ - R ⋅ (i1 + I2’)

i1 and i2 calculation as a function of ”VIN” on Pin 19

-

A1

Amplifier

:

VVSIN1=

RC

dr1

=

125070=

21

dr

:

dynamic resistance

=

λ

I

- A2 Amplifier :

i2

VS2

=

2d1r2=

1

54

⇔

i2

VIN

=

VS1

VIN

⋅

i2

VS1

=

0.395

⇒ i2 = 0.39 VIN, i2 is in phase with VIN therefore :

i3 = -i2 = -0.39 VIN

- A3 Amplifier :

i1

=

i3







− VC

Aλ

+

1

2







=

-

0.39

VIN







− VC

Aλ

+

1

2







”VIN” always leads the ”i1” by 180, only the ampli-

tude of i1 is a function of VC (see Figure 23).

-

VOUT

VIN

=-

R

i1 (1 + j R1C1ω) + i2

1 + j (R1 + R) C1ω

-

i1

=

-

0.39

VIN

i

 2

−

VC

4λ







and

i2

=

0.39

VIN

The Figure 24 illustrates the characteristics of

V18/VIN phase versus VC.

- Phase variation determined by VC falls between

+24o and +135o range

- The gain is higher than 10dB. The Pin 18 output

signal of 30 to 40dB has a rectangularcomponent

(see Figure 24).

Figure 22

18

i 18

R1

17

i1

R

V18 C1

i2

i

18

17

i 18

i1

R

V18

Z

i 2’

Figure 23 : Vector Representation of V18/VIN

V18 @ i 1 = 0

Ri1

R ( i1 + i2)

VOUT

VIN

phase variation = f(VC)

+136°

-45° VIN

Ri 2

V18 @ i 1 (Max. )

R (i1 + i2)

13/46

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