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TEA2029

APPLICATION NOTE

STMicroelectronics 

TEA2028 - TEA2029 APPLICATION NOTE

This amplitude changing modifies the open-loop

system gain and therefore the damping coefficient

and the locking time constant.

The device will be in short time constant mode

under the following two conditions :

- VCR Mode or SCART Connector Mode :

This mode is enabled by a low state on Pin 23.

V23 < 2.1V.

- Transmitter search and tunning.

In order to accelerate the capture, a ”Video Iden-

tification” stage will detect the presence or the

absence of a video signal on input Pin 27, and

deliver accordingly a signal called ”Mute”.

V.3.5 - Video identification stage

This stage will detect the coincidence between the

line sync pulse (if present) and a 2µs pulse issued

from the logic block. This 2µs pulse at line fre-

quency is positionned at the center of line sync

pulse when the first loop ”ϕ1” is locked.

This sampled detection is stored by an external

capacitor connected to Pin 25. The video recogni-

tion status is also available on Pin 24 so as to

enable Sound Muting during station search proc-

ess and the inhibition of Automatic Frequency Tun-

ing.

V.3.5.1 - Block diagram

Figure 28

+

ϕ1

LS

&

2µs

LS

&

IC

750µA

ID

i C(25)

500µA 25

Comparator

Pin

24

C25

4.7nF

4.6V

Frame

Logic

The video recognition signal is delivered by a hys-

teresis comparator.

The recognition time ”TR” is adjustable by an exter-

nal capacitor, as soon as ϕ1 is locked :

-

IC25(AV) =

IC

⋅

2µs

64µs

and :

-

TR

=

C25

⋅

VH

IC25(AV)

=

1.96

⋅

105

⋅

C25

with C25 = 4.7nF ⇒ TR = 1ms

(which is clearly quite fast)

Figure 29

ϕ1

Line Sync.

LS

2µs

IC(25)

IC

4.7µs

2µs

with Video

IC(25)

without Video

ID

Mute

Output

1

0

VHYST = 0.3V

VL VH

V25

4.6V

V.3.6 - Characteristics of loop φ1

V.3.6.1 - Locking accuracy

Let’s study the phase error ”ϕOUT - ϕIN” under

steady state conditions :

The open-loop gain is :

-

T(p)

=

AB f(p)

f

Where :

A = 0.16mA/rd (long time constant)

A = 0.47mA/rd (short time constant)

B = 0.7kHz/V or B = 4.4 103rd/s

-

f(p)

=

R

⋅

(1

+

1 + τ1 p

τ2 p) (1 +

τ3

p)

Where : R = Dynamic input resistance of VCO.

If a phase step of ∆ϕ is applied to the input, the

following would be obtained as a function of (p) :

ΦIN(p)

=

∆Φ

p

Using the last value theorem : lim f(t) = lim p . f(p)

Let’s calculate lim (ϕIN − ϕOUT)

p→0

- The closed-loop gain is :

-

H(p)

=

1

T(p)

+ T(p)

=

p

ABf(p)

+ ABf(p)

=

ΦOUT(p)

ΦIN(p)

that is

: lim p (ΦIN −

p→0

ΦOUT)

= lim

p−>0

p∆Φ

p + AB f(0)

→0

15/46

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