carrier without disruption due to the modulation.

Dual frequency operation is made possible by syn-

thesising the carrier reference frequency thus sav-

ing the need for two extra crystals. Dual VCXO can

also be software selected (SYN bit of CR3 in

TDA8204) with external crystal (Pin XC1/XC2) for

new standards. Selection between XC1 and XC2

is done with bit "IBG" in CR3 register of TDA8204

(IBG = 0 XC1 selected, IBG = 1 XC2 selected).

The standards switch controls operation of the

QSPK demodulator at either 6.552MHz or

5.85MHz. This can be controlled via the I

the decoder set into automatic mode in which it

determines the standard by alternately trying to

lock to the two systems.

On chip low pass filters recover the in-phase and

quadrature data channels which are then sliced by

comparators. The symbol clock is recovered from

this data and used to sample and re-time it. The

two data channels are then decoded and serialized

to obtain the NICAM-728 data which is then passed

on to the NICAM decoder in the TDA8204.

After processing the NICAM into a digital bit-stream

in the TDA8204, the data is passed back to the

TDA8205 for the analog functions of the DACs to

be performed.

Conversion of the pulse width modulated bit

streams to analog takes place and is followed by

low pass filtering which removes high frequency

quantising noise and performs J-17 de-emphasis.

The DACs signal level can be adjusted to match

the reserve sound signal level.

tained by selection of appropriate resistor on

Pin RG.

Once the analog audio has been recovered, certain

source switch functions are performed. If the NI-

CAM signal fails and if the reserve sound flag (C4),

of SRO register, is set the reserve sound switch

automatically selects Mono Audio Input. If the re-

serve sound flag (C4) is reset, the reserve sound

switch will not change and the audio outputs will be

muted (DAC outputs muted).

If the NICAM signal only carries data, Mono Audio

Input is selected. The reserve sound switch can be

forced to select Mono Audio Input via I

Bit FS0 = 1 and FS1 =0 of CR3 Register.

This can be used in the case of NICAM marginal

reception. To select Stereo Left and Right Audio

Input Bit FS0 = 0 and FS1 = 1 of CR3 Register must

be selected. The outputs from this reserve sound

switch are available on Audio mutable output left

and right, and are internaly connected to the audio

matrix.

A simple audio switching matrix is provided inter-

nally for flexible control over the audio source and

destination selection.

Audio signal left and right coming from the reserve

sound switch and the external audio input left and

right can be switched to the audio outputs left and

right .

DAC and auxiliary audio outputs can be muted. An

additional +6dB gain can be applied to raise the

m at ion s ee Sof t wa re Specification chap-

ter (III.5.3/TDA8204).

The DAC outputs are automatically muted under

the following conditions

- loss of frame alignement

- the bit error rate (Ber) is > error rate limit

- NICAM signal is conveying M1 only. The right

DAC is muted unless M1 has been selected to be

on both DAC outputs.

- NICAM signal is conveying data only.

For test purposes, the DAC outputs can be un-

muted by forcing the bi-directional mute Pin 25 of

TDA8204 or via I

ABSOLUTE MAXIMUM RATINGS

Symbol

Parameter

Value

Unit

Supply Voltage

15

V

Supply Voltage

7

V

Total Power Dissipation

1.2

W

Operating Temperature Range

0, + 70

Storage Temperature Range

-20, + 150

THERMAL DATA

Symbol

Parameter

Value

Unit

Thermal Resistance Junction-Ambient

Max.

67

TDA8205

3/8