TEA2029 STMICROELECTRONICS [STMicroelectronics], TEA2029 Datasheet - Page 13

• Manufacturer Part Number: TEA2029
• Description: APPLICATION NOTE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Thus, a variable (24
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 V
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 1 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
a function of V
V
To start with, the ”V
is taken as reference parameter.
The dynamic representation of the output stage
can be depicted as below (Figure 22).
with : I
R1 C1
and Z = R1 +
R1C1 network produces -45
respect to ”i2”, around 500kHz.
i
- A1 Amplifier :
- A2 Amplifier :
- A3 Amplifier :
1
22
dr : dynamic resistance =
i
i
V
and i
3
1
i
2
S2
= -i
= i
=
i
2
V
=
3
2
= 0.39 V
K
2
2
’ =
C
calculation as a function of ”V
2dr
= -0.39 V
= 1
where K is a non-linear coefficient
1
A
1
V
2
=
C
j C
22
j R1 C1
54
IN
1
1
V
V
V
i
.
i
2
, i
1
2
2
18
S1
’ =
IN
IN
2
<< R
=
is in phase with V
C
o
= - 0.39 V
1
V
” voltage of comparator ”A3”
R
dr
to + 135
- R (i
i
i
22
2
2
IN
C
1
(at f = 500kHz)
j
whose value of 5.6V 0.7
=
V
V
1200
i
1
I
o
S1
57
IN
+ I
o
phase lag of ”i” with
IN
i
) phase lead with a
2
2
’
= 21
V
’)
i
2
S1
A
V
IN
= 0.395
IN
C
” on Pin 19
therefore :
1
2
V
V
18
IN
as
”V
tude of i
-
- i
The Figure 24 illustrates the characteristics of
V
- Phase variation determined by V
- The gain is higher than 10dB. The Pin 18 output
Figure 22
Figure 23 : Vector Representation of V
TEA2028 - TEA2029 APPLICATION NOTE
18
+24
signal of 30 to 40dB has a rectangularcomponent
(see Figure 24).
IN
V
1
V
/V
” always leads the ”i
OUT
= - 0.39 V
V
IN
Ri
o
IN
18
R ( i + i )
1
and +135
phase versus V
1
i
@ i
= - R
1
1
is a function of V
i
1
1
= 0
2
18
i
IN
1
1
18
i
o
R
1
18
2
i
range
j R
i
R
18
j R
+136
V
4
1
Ri
V
C
1
C
-45
18
C
1
V
2
.
V
V
” by 180, only the ampli-
R C
OUT
and i
1
R1
C
i
18
IN
V
C1
(see Figure 23).
IN
1
phase variation = f(V
2
i
2
Z
= 0.39 V
V
17
18
R (i + i )
17
C
@ i
falls between
1
i ’
2
18
1 (Max. )
i
2
IN
2
/V
IN
13/46
C
)