Philips tda8505 DATASHEETS

INTEGRATED CIRCUITS

DATA SH EET

TDA8505

SECAM encoder

Preliminary specification
Supersedes data of May 1993
File under Integrated Circuits, IC02

Philips Semiconductors

July 1994

Philips Semiconductors Preliminary specification

SECAM encoder TDA8505

FEATURES

• Two input stages, R, G, B and Y, −(R−Y), −(B−Y) with
multiplexing.

• Chrominance processing, highly integrated, includes
vertical identification, low frequency pre-emphasis and
high frequency pre-emphasis (anti-Cloche) and
bandpass filter.

• Fully controlled FM modulator which produces a signal
in accordance with the SECAM standard without
adjustments.

• Two reference oscillators, one for D'R f
and one for D'B f0 (4.250 MHz). These oscillators are
tuned by PLL loop with the frequency of the line sync as
reference. Crystal tuning, or tuning by external
reference source, of the reference oscillators is
possible.

• Output stages, CVBS and separated Y + SYNC and
CHROMA. For CVBS output, signal amplitude 2 V (p−p)
nominal, thus only an external emitter follower is
required for 75 Ω driving.

• Sync separator circuit and pulse shaper, to generate the
required pulses for the processing, line, frame, FH/2 and
chrominance blanking.

(4.40625 MHz)

0

GENERAL DESCRIPTION

The TDA8505 is a highly integrated SECAM encoding IC
that is designed for use in all applications that require
transformation of R, G and B signals or Y, U and V signals
to a standard SECAM signal.

The specification of the input signals is fully compatible
with those of the TDA8501 PAL/NTSC encoder.

• A 3-level sandcastle pulse is generated for PAL/NTSC
to SECAM transcoding.

• FH/2 input for locking with another decoder.

• Colour killing on the internal colour difference signals.

• Internal bandgap reference.

ORDERING INFORMATION

TYPE NUMBER

PINS PIN POSITION MATERIAL CODE

TDA8505 32 SDIP32 plastic SOT232-1

PACKAGE

July 1994 2

Philips Semiconductors Preliminary specification

SECAM encoder TDA8505

BLOCK DIAGRAM

Y+SYNC

1 V (p p)

470 nF

100 Ω

nF

6.8

15

Y+SYNC output

LPFDB output

2 V (p-p)

25

LINE

DELAY

ns

650

23

input

Y+SYNC

notch

22

output

21

MLA951 - 3

CVBS 2 V (p p)

output

XTAL/PLL

VIDENT

input

26

1 µF

3.9 kΩ

270 pF

output

VCO4.25

27

1 nF

13

LPFDR output

4.7 µF

4.7 µF

1.2 kΩ

2.2 kΩ

100 nF

output

LPF 4.4

22 nF

output

LPF4.25

24

31

8

VCO

4.406 MHz

282

DIVIDER

PHASE

DETECTOR

SWITCH

32

10

30

VCO

4.25 MHz

272

DIVIDER

PHASE

DETECTOR

SYNC

SEPARATOR

29

28

PHASE

PULSE

GENERATOR

4

DETECTOR

SANDCASTLE

19external power

20

PHASE

DETECTOR

TDA8505

ADDER

12

FRAME

IDENTI-

FICATION

7

2

CL/BL

BUFFER

FM

PHASE

MODULATOR

GAIN

ADDER

LIMITER

CLAMP

FILTER

LF PRE-

EMPHASIS

LOW-PASS

MATRIX

SWITCH

SEQUENCE

CL/BL

9

2 kΩ

SWITCH

CL/BL

11

ADDER

18

BLANKING

CHROMINANCE

16

FILTER

CLOCHE BANDPASS

ref

V

CL/BL CL/BL CL/BL

14

FADJ

17

V

6

5

3

1

output

chrominance

nF

220

FLT output

22

nF

kΩ

4.7

1.8 kΩ

ref

TEST

47

nF

47

nF

47

nF

22 kΩ

22 nF

47

µF

reference

input

luminance

(B Y)

inputs

(R Y)

colour difference

output

voltage

handbook, full pagewidth

Fig.1 Block diagram.

22

nF

47 µF

SSA

DDA

V

V

July 1994 3

V

DDD

100 nF

SSD

V

22 nF

sync

input

composite

input

FH/2 input

colour killing

ext

output

sandcastle

supply (V )

multiplexer

control input

(Y/Y SYNC)

47

RED

input

control input

nF

GREEN

input

47

47

nF

nF

input

BLUE

Philips Semiconductors Preliminary specification

SECAM encoder TDA8505

PINNING

D'R and D'B are the colour difference signals at the output of the multiplexer circuit; D'R = −1.9(R−Y) and
D'B = +1.5(B−Y), for an EBU bar of 75% the amplitudes are equal.

SYMBOL PIN DESCRIPTION

−(R−Y) 1 colour difference input signal, for EBU bar of 75% 1.05 V (peak-to-peak value)
MCONTR 2 multiplexer control; input HIGH = RGB, input LOW = −(R−Y), −(B−Y) and Y

−(B−Y) 3 colour difference input signal, for EBU bar of 75% 1.33 V (peak-to-peak value)
FH/2 4 line pulse input divided-by-2 for synchronizing two or more encoders; when not used this

pin is connected to ground
Y 5 luminance input signal 1 V nominal without sync
TEST 6 test pin; must be connected to V
R 7 RED input signal for EBU bar of 75% 0.7 V (peak-to-peak value)
V

DDA

8 analog supply voltage for encoder part; 5 V nominal
G 9 GREEN input signal for EBU bar of 75% 0.7 V (peak-to-peak value)
V

SSA

10 analog ground
B 11 BLUE input signal for EBU bar of 75% 0.7 V (peak-to-peak value)
Y/Y+SYNC 12 when this control input is LOW, Y without sync is connected to pin 5, input blanking at

pin 5 is active; when input is HIGH, Y+SYNC is connected to pin 5, input blanking at pin 5

is not active
LPFDR 13 modulator control loop filter output; black level of D'R = 4.40625 MHz
FADJ 14 adjustment pin for 4.286 MHz of HF pre-emphasis filter
LPFDB 15 modulator control loop filter output; black level of D'B = 4.250 MHz
FLT 16 filter tuning loop capacitor output
V

ref

17 2.5 V internal reference voltage output
CHROMA 18 chrominance output, amplitude corresponds with Y+SYNC at the output of the delay line
V

ext

19 external power supply for sandcastle generation; when not used this pin is connected to

ground
SAND 20 3-level sandcastle output pulse
CVBS 21 composite SECAM output 2 V (peak-to-peak value) nominal
NOTCH 22 Y+SYNC output after an internal resistor of 2 kΩ; a notch filter can be connected
Y+SYNC IN 23 Y+SYNC input, connected to the output of the delay line
LPF4.4 24 loop filter output for 4.40625 MHz reference oscillator
Y+SYNC OUT 25 Y+SYNC output, 2 V (peak-to-peak value) nominal, connected to the input of the

delay line
XTAL/PLL

VIDENT

26 control pin; input HIGH = crystal tuning, input LOW = PLL tuning, both without vertical

identification, 2.5 V = PLL tuning with vertical identification
VCO4.25 27 when used for PLL tuning a capacitor is connected; when used for crystal tuning a crystal

has to be connected (in series with a capacitor)
COLKIL 28 colour killing; input HIGH = active, internal colour difference signals are blanked
CS 29 composite sync input, 0.3 V (peak-to-peak value) nominal

(pin 8), or left open-circuit

CC

July 1994 4

Philips Semiconductors Preliminary specification

SECAM encoder TDA8505

SYMBOL PIN DESCRIPTION

V

SSD

LPF4.25 31 loop filter output for 4.25 MHz reference oscillator; connected to pin 17 (V

V

DDD

30 digital ground

external tuning by crystal or signal source

32 supply voltage for the digital part

) when

ref

handbook, halfpage

MCONTR

Y/Y SYNC

(R Y)

(B Y)

FH/2

TEST

V

DDA

V

SSA

LPFDR

FADJ

LPFDB

FLT

1
2
3
4

Y

5
6

R

7
8

9
10
11
12

13
14
15
16

TDA8505

MLA952 - 3

G

B

V

DDD

32
31

LPF4.25
V

30

SSD

CS

29

COLKIL

28

VCO4.25

27

XTAL/PLL

26

VIDENT
Y+SYNC OUT

25

LPF4.4

24
23

Y+SYNC IN
NOTCH

22
21

CVBS
SAND

20

V

19

ext

18

CHROMA
V

17

ref

July 1994 5

Fig.2 Pin configuration.

Philips Semiconductors Preliminary specification

SECAM encoder TDA8505

FUNCTIONAL DESCRIPTION

The following three important circuits are integrated:

• Encoder circuit

• Modulator control circuit

• Sync separator and pulse shaper.

Encoder circuit

I

NPUT STAGE

R, G and B inputs are connected to the matrix via a
clamping and a blanking circuit.

For an EBU colour bar of 75% the amplitude of the signal
must be 0.7 V (peak-to-peak value). The outputs of the
matrix are Y, D'R and D'B.

The second part of the input stage contains inputs for
colour difference signals and a luminance signal. The
condition for 75% colour bar is

−(R−Y) = 1.05 V (peak-to-peak value) at pin 1,

−(B−Y) = 1.33 V (peak-to-peak value) at pin 3 and

Y = 1 V (peak-to-peak value) without sync at pin 5. After
clamping and blanking the amplitude and polarity are
corrected such that the signals are equal to the signals of
the matrix output. Signals are connected to a switch. Fast
switching between the two input parts is possible by the
multiplexer control pin (pin 2).

The Y output signal of the multiplexer is added to the sync
pulse of the sync separator.

The Y input (pin 5) is different to the other 5 inputs. The
timing of the internal clamping is after the sync period and
there is no vertical blanking.

The input blanking of Y can be switched off by a HIGH at
pin 12, and the internal sync separator signal is not added
to the Y signal. In this way the Y+SYNC is allowed at pin 5
and after clamping internally connected directly to pin 25.

The colour difference signals are switched sequentially by
H/2 and fed to the low frequency pre-emphasis circuit.

The colour-killing input signal at pin 28 can be used for
completely blanking the internal colour difference signals
at the input of the low frequency pre-emphasis filter.

LOW FREQUENCY PRE-EMPHASIS
This filter is fully integrated, Fig.3 illustrates the nominal

response.
The transfer is guaranteed within the illustrated area for

the whole ambient temperature range by a compensation
circuit.

H

(dB)

4

2

0

2

4

6

8

10

4

10

5

10

handbook, full pagewidth

Fig.3 Nominal response for the low frequency pre-emphasis filter.

July 1994 6

MLA953 - 1

6

10

f (Hz)

7

10

Philips Semiconductors Preliminary specification

SECAM encoder TDA8505

VERTICAL IDENTIFICATION
After the low frequency pre-emphasis the signal is

clamped and, if desired the vertical identification sawtooth
waveform can be added. The generation of the vertical
identification is switched on/off by the logic level input at
pin 26.

Figure 4 shows the sawtooth waveform at the input of the
FM modulator with the corresponding frequency values
after modulation.

Vertical identification is only possible if PLL tuning is
selected.

AIN + LIMITER

G
The gain of this amplifier is sequentially switched, so that

the amplitude of D'R is 280/230 times the amplitude of D'B
(based on an EBU colour bar). The signal is limited at a
lower and upper level to ensure that the FM modulator
frequencies are always between 3.9 MHz and 4.756 MHz.
A DC offset between D'R and D'B is added which
corresponds with the limiter levels.

MODULATOR

FM
The signal of the gain + limiter stage is fed to the FM

modulator.

level of D'R. The modulator control also sets the DC level
at pin 15 to adjust the FM frequency to 4.250 MHz at the
black level of D'B.

At the start of every line the FM modulator is stopped and
is started again by a short duration pulse of the pulse
shaper. These stop/start pulses are operating such that
after two lines starting in the same phase, the start phase
of the third line is shifted 180 degrees. This sequence is
inverted during each vertical blanking.

The FM signal is fed to the internal HF pre-emphasis filter.

HF PRE-EMPHASIS AND BANDPASS FILTER
An HF pre-emphasis filter combined with a bandpass filter

is integrated.
Figures 5 and 6 illustrate the frequency response. Two

resistors in series with a potentiometer at pin 14 adjusts
the frequency to 4.286 MHz with a tolerance of ±20 kHz.

A tuning circuit integrated with an external capacitor
connected to pin 16 guarantees a stable frequency
response for the whole temperature range.

The output of the bandpass filter is connected directly to
the chrominance blanking circuit.

The modulator control adjusts the DC level at pin 13 to set
the frequency of the FM signal to 4.406 MHz at the black

handbook, full pagewidth

15 sµ

5 sµ

D'R

18 sµ

Fig.4 Vertical identification sawtooth waveform input.

6 sµ

frequency

after

64 µs64 µs

D'B

MLA954

modulation

4.756 MHz
35 kHz

4.406 MHz

4.250 MHz

3.90 MHz

35 kHz

July 1994 7

Philips Semiconductors Preliminary specification

SECAM encoder TDA8505

H

(dB)

100

0

20

40

60

80

5

10

6

10

7

10

f (Hz)

handbook, full pagewidth

Fig.5 Frequency response of the HF pre-emphasis and bandpass filter; H as a function of frequency (1).

MLA955 - 1

8

10

16

handbook, full pagewidth

H

(dB)

14

12

10

8

6

4

2

0

2

3.7 4.1 4.5

3.9 4.3 4.7

Fig.6 Frequency response of the HF pre-emphasis and bandpass filter; H as a function of frequency (2).

MLA956 - 1

upper limit

nominal

lower limit

f (MHz)

4.9

July 1994 8

Philips Semiconductors Preliminary specification

SECAM encoder TDA8505

CHROMINANCE BLANKING
The chrominance signal is blanked by the internally

generated chrominance blanking pulse. The output of this
blanking stage is connected to the chrominance and
CVBS output circuits.

Y+SYNC, CVBS,

AND CHROMA OUTPUTS

The Y output signal of the matrix is added to the composite
sync signal of the sync separator. The output of this adder
at pin 25 is connected to the input of an external delay line
which is necessary for correct timing of the Y+SYNC signal
corresponding with the chrominance signal. The signal
amplitude at pin 25 is 2 V (peak-to-peak value) nominal,
so at the output of the delay line Y+SYNC is
1 V (peak-to-peak value).

The delay line has to be DC-coupled between
pins 25 and 23 to ensure the required DC level at
pin 23. The output resistor of the delay line has to be
connected to pin 17 where (V

= 2.5 V).

ref

The output of the delay line is connected to pin 23 which is
the input of a buffer operational amplifier. The output of the
buffer operational amplifier is connected to pin 22 and to
the CVBS adder stage via an internal resistor of 2 kΩ. An
external notch filter can be connected to pin 22. The CVBS
signal amplitude output at pin 21 is 2 V (peak-to-peak
value) nominal. An external emitter follower is used to
provide a 75 Ω output load.

The outputs of the 272 divider are also used for pulse
shaping.

Within the vertical blanking period, another two Phase
Locked Loops (PLLs) synchronizes the FM modulator
during two lines with the 4.406 MHz reference VCO and
during the following 2 lines with the 4.250 MHz reference
VCO. The loop filters are connected to pins 13 and 15
respectively.

It is necessary to use low-leakage capacitors for these
loop filters.

T

UNING BY CRYSTAL OR EXTERNAL SIGNAL SOURCE

When the frequency of the sync pulse at pin 29 is not
stable or is incorrect it is possible to tune the FM modulator
using an external 4.250 MHz crystal connected to pin 27.
The 4.25 MHz loop at pin 31 has to be connected to pin 17
(V

). A stable line frequency reference is generated by

ref

the 272 divider circuit which is used for the 4.406 MHz
reference loop.

An external signal source, instead of a crystal, can be
connected at pin 27 via a capacitor in series with a resistor.

The minimum AC current of 50 µA is determined by the
resistor values (R

int+Rext

) and the output voltage of the

signal source (see Fig.7).

When crystal tuning is used no vertical identification
is possible.

The amplitude of the chrominance output signal which is
connected to pin 18 corresponds with the Y+SYNC signal
at the output of the delay line.

Modulator control circuit

The modulator control circuit has two tuning modes which
are controlled by the input at pin 26:

• Tuning by line frequency

• Tuning by crystal or external signal source.

UNING BY LINE FREQUENCY

T
Two reference voltage controlled oscillators (VCOs) are

integrated, the 4.4 MHz VCO with an internal capacitor
and the 4.25 MHz VCO with an external capacitor at
pin 27.

A PLL loop with divider circuits directly couples the
frequencies of the two VCOs with the line frequency of the
sync separator sync signal.

The loop filter for the 4.40625 MHz reference is at pin 24
and the loop filter for the 4.250 MHz reference is at pin 31.

July 1994 9

Crystal tuning is recommended for VTR signals.

handbook, halfpage

TDA8505

OSCILLATOR

R

int

800Ω

27

R

ext

MSA732 - 1

µ

I 50 A

1 nF

Fig.7 Tuning circuit for external signal source.

signal

source
V (p-p)