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TDA9829T

Downconverter for DVB

Philips Electronics 

Philips Semiconductors

Downconverter for DVB

Product specification

TDA9829T

FUNCTIONAL DESCRIPTION

Vision IF amplifier

The vision IF amplifier consists of three AC-coupled

differential amplifier stages. Each differential stage

comprises a feedback network controlled by emitter

degeneration to control the IF gain.

VCO, Travelling Wave Divider (TWD) and AFC

The VCO operates with a resonance circuit (with L and C

in parallel) at double the IF frequency plus symbol

frequency. The VCO is controlled by integrated variable

capacitors. The control voltage required to tune the VCO

from its free-running frequency to its actual frequency is

fed to the capacitors. This control voltage is amplified and

converted into a current which represents the AFC output

signal. At centre frequency the AFC output current is equal

to zero.

The oscillator signal is divided-by-two with a TWD which

generates a differential output signal for downconverting

the IF signal.

DVB mixer

The gain controlled DVB-IF signal is downconverted to the

symbol frequency by use of a four quadrant multiplier.

The conversion signal is provided by the VCO and TWD.

DVB AGC and tuner AGC

The AGC detector charges/discharges the AGC capacitor

to the required voltage for setting the IF and tuner gain in

order to keep the DVB signal at a constant level.

A peak detector is used for the DVB AGC. The peak value

of (digital) the QAM signal is detected and controlled to a

constant value by the variable gain IF amplifier.

The detector bandwidth is adapted to the symbol

frequency (3 to 11 MHz). The external AGC time constant

is given by the IF AGC capacitor at pin 18.

The AGC capacitor voltage is transferred to an internal IF

control signal, and is fed to the tuner AGC to generate the

tuner AGC output current (open-collector output).

The tuner AGC takeover point can be adjusted. This

allows the tuner and the SWIF filter to be matched to

achieve the optimum IF input level.

The DVB output signal (VoDVB) can be adjusted in a range

of ±3 dB by a control voltage (∆Vadj) at pin 9. The internal

AGC can be switched off at pin 6 and the IF gain can be

controlled by an external voltage at pin 8. The tuner AGC

is active in both instances.

DVB output amplifier

The output amplifier for the DVB signal has a high

bandwidth and delivers a 2 V (p-p) signal. The amplifier

can be switched to a mute state forced by the signal at

pin 20.

Internal voltage stabilizer

A band gap circuit internally generates a voltage of

approximately 1.25 V, independent of supply voltage and

temperature. A voltage regulator circuit, connected to this

voltage, produces a constant voltage of 3.6 V which is

used as an internal reference voltage.

LIMITING VALUES

In accordance with the Absolute Maximum Rating System (IEC 134).

SYMBOL

VP

Vn

tsc(max)

V12

Tstg

Tamb

Ves

PARAMETER

supply voltage (pin 19)

voltage at pins

1 to 10, 13, 14 and 18 to 20

maximum short-circuit time

tuner AGC output voltage

storage temperature

operating ambient temperature

electrostatic handling voltage

CONDITIONS

MIN.

maximum chip temperature of 125 °C 0

0

MAX. UNIT

5.5 V

VP

V

machine model class B

−

10

s

0

13.2 V

−25 +150 °C

−20 +70 °C

−300 +300 V

1998 Nov 09

5

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