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PDF TDA8349A Data sheet ( Hoja de datos )
| Número de pieza | TDA8349A | |
| Descripción | Multistandard IF amplifier and demodulator | |
| Fabricantes | NXP Semiconductors | |
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INTEGRATED CIRCUITS
DATA SHEET
TDA8349A
Multistandard IF amplifier and
demodulator
Product specification
File under Integrated Circuits, IC02
February 1991
1 page  
Philips Semiconductors
Multistandard IF amplifier and demodulator
Product specification
TDA8349A
bandgap also reduces the supply ripple on the video
output to values less than −30 dB. The video amplifier has
a typical bandwidth of 10 MHz which allows application for
all new video standards with bandwidths of up to 10 to
12 MHz. The video output signal has an amplitude of
2 V (p-p). White spot protection comprises a white spot
clamp system combined with a delayed-action inverter
which is also highly resistant to high sound carriers. A
switchable DC shift for positively modulated IF signals
ensures correct signal handling. This switching is obtained
via pin 20, which is the same pin used for switching the
demodulation polarity in the demodulator.
The circuit also has a noise clamp which prevents the
video output becoming less than ±400 mV below the top
sync level at noise peaks. The output buffer of the video
amplifier consists of a class A/B circuit which can handle
large source as well as large sink currents. This makes the
circuit more flexible in several applications with one or
more ceramic filters connected to this output buffer.
AGC control circuit
This converts the AGC detector voltage (pin 5) into a
current signal which controls the gain of the IF amplifier. It
also provides a tuner AGC control output from pin 4,
current limiting is incorporated to prevent internal damage.
The AGC starting point is adjusted by a voltage between 3
and 5 V for pnp tuners and between 7 and 9 V for npn
tuners via pin 3.
AGC circuit
A new AGC system has been designed for the AGC. It will
be a top sync-detector for negatively modulated signals
and a top white level AGC for positively modulated signals.
For optimal flexibility reasons the load and unload currents
of the AGC are chosen such that both, a relatively fast set,
as well as a set with a low tilt are possible for positive (L)
and negative (B/G) modulated signals. For this reason a tilt
ratio between positive (L) and negative (B/G) of
approximately 3:1 has been chosen. This means that in a
fast set the choice of a typical tilt for negatively modulated
signals of 2% will obtain a typical tilt for positively
modulated signals (L) of 6%. For a digital set which
requires a small tilt the choice of tilt can be a factor of 5 or
10 smaller by increasing the AGC capacitor.
The chosen AGC currents:
MODE
B/G
L
MAC(positive)
MAC(negative)
UNLOAD CURRENT
50 µA
500 nA (note 1)
200 nA
500 nA
LOAD CURRENT
1.5 mA
1.5 mA
1.5 mA
1.5 mA
TILT AT 2.2 µF
typ. 0.5% (line tilt)
typ. 1.5% (field tilt)
typ. 1.2% (frame tilt)
typ. 1.5% (field tilt)
Note
1. As long as no signal has been identified by the identification detector the unload current will be 50 µA.
Switching between the first three modes can be achieved
by the system switch. This is a 3-level switch which when
grounded selects B/G; open or 5 V selects L, and with pin
20 connected to VCC selects positively modulated MAC.
The IC operates in a fourth mode if the identification
capacitor at pin 19 is connected to VCC, it can be used for
negatively modulated MAC.
During channel switching a situation can occur that
requires the AGC to increase the gain more than for
example 50 dB. If this increase of gain has to be done for
a positively modulated (L) signal, it will be achieved by the
500 nA load current and is therefore extremely slow.
Because the identification information can be used to
indicate that the signal is too small, in this event the
identification circuit will mute, it is possible to increase the
positive unload current to the same value as that used for
negatively modulated signals. This switching is fully
automatic and cannot be switched off.
AFC circuit
The AFC circuit consists of a demodulator stage which is
fed with signals 90° out of phase. A very accurate internally
realized 90° phase shift circuit makes it possible to use the
demodulator IF regenerator tuned circuit for tuning the
AFC circuit. To prevent video ripple on the AFC output
voltage a sample-and-hold circuit is used for negatively
modulated signals. The output signal of the demodulator is
sampled during sync level of the video signal and will be
stored with the aid of an external capacitor.
February 1991
5
5 Page 
Philips Semiconductors
Multistandard IF amplifier and demodulator
Product specification
TDA8349A
Notes
1. All input signals are measured in RMS values at 100% carrier level and a frequency of 38.9 MHz.
2. On set AGC.
3. Input impedance selected so that a SAW filter can be applied without extra components.
4. Measured with 0 dB = 200 µV.
5. Measured at 10 mV(RMS) top sync input signal and the video output unloaded.
6. Projected zero point with internally switched demodulator.
7. With the AGC switch switched to ground, for the B/G standard, or with the identification capacitor switched to VCC
for the negative MAC standard.
8. With the AGC switch switched open for the L standard, or switched to VCC for the positive MAC standard.
9. Measured in accordance with the test line given in Fig.8.
- The differential gain is expressed as a percentage of the difference in peak amplitudes between the largest and
smallest value relative to the subcarrier amplitude at blanking level.
- The differential phase is defined as the difference in degrees between the phase angle of the 4.4 MHz signal at
20% and 80% luminance signal.
10. Measured in accordance with the test line shown in Fig.9.
The non-linearity is measured by comparing the differences between adjacent pairs of six luminance levels that make
up the 5 step staircase. The measurement result is the largest percentage deviation in adjacent step values. The sign
is always positive.
11. Measured with a 75 Ω source: S ⁄ N = 20 log -V----n----(-V-R---o--M--b----Sl-a---)-c--a-k----t--t-Bo-----w-=----h-5--i-t--eM-----H----z--
12. The internal circuit of pin 20 behaves as an internal voltage source of 4.5 V with an input resistance of 15 kΩ. Using
the system switch three conditions can be obtained:
Negative modulation with top sync level AGC. This is achieved with pin 20 connected to ground.
Positive modulation with white level AGC. This is achieved with pin 20 open, or connected to 5 V.
Positive modulation with top white AGC and an increased time constant for MAC signals. This is achieved with pin
20 connected to VCC.
13. Measured with a capacitor of 2.2 µF connected to pin 5. A step is made from 200 µV to 80 mV input signals.
14. Measured with a capacitor of 2.2 µF connected to pin 5. A step is made from 80 mV to 200 µV input signals.
15. It is possible to adjust the tuner AGC over the whole AGC range of the IF amplifier for both pnp and npn tuners. Tuner
AGC starting point is defined as an output current of 0.2 mA for pnp and 1.8 mA for npn, in an application with a
resistance of 6 kΩ to VP at pin 4.
16. Crosstalk is defined as: 20 log V----V-o---uo---nw---w-a----an---nt--e-t--ed---d--v---i-v-d--i-de---eo----o-b----bl-a--l-ac---k-c----k-t---o--t-o---w-----w-h---hi-t--ei--t-e-- measured at 4.4 MHz
17. The video switch is controlled by a voltage on pin 7. The switching level is approximately 1.4 V. With pin 7 open-circuit
internal video is selected; with pin 7 pulled to ground external video is selected.
18. Measurement taken with an input 10 mV(RMS). The unloaded Q factor of the reference tuned circuit is 70.
19. Switching off the AFC is obtained by a voltage of less than 2 V on pin 6. Normally this is achieved by pulling pin 6 to
ground.
20. Switching to the normal analog AFC mode can be done by pulling pin 9 to a voltage above 10.2 V. Normally this is
achieved by pulling pin 9 to VP.
The inverse analog AFC mode can only be obtained by a voltage of between 8 and 10 V applied to pin 9.
February 1991
11
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