Operation Manual Part 1

Digital Liquid Cooled UHF
TV Equipment
Detailed operational description
9946 V1
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preliminary
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Information contained is this document is confidential, is THOMSON property and cannot be disclosed in whatever form without prior written authorization of THOMSON.
2.2. Transmission function
2.2.1. Operational description of digital exciter
The exciter (EMB) transposes the input base-band MPEG signal into an RF signal using a local
frequency oscillator from a synthesiser.
The incoming data stream signal (MPEG2-TS) is processed by the Channel Modulator (TS card),
depending on the standard (DVB-T or ATSC), which provides an output complex digital signal in the
form of two parallel I and Q digital signals and a clock reference.
These I & Q signals are then processed by the DAP (Digital adaptative pre-correction):
♦ Optional Clipping,
♦ Optional Adaptive Linear Equalisation (ALE),
♦ Adaptive non-linear correction.
With the digital filter option, as long as the magnitude of the vector is less than a given threshold, the
vector remains unchanged. For magnitudes higher than the threshold, the vector is replaced by the
specific complex value of the threshold. The process does not influence the phase.
The linearity correction ALE, as well as the non linearity correction (LUT) are based on the following
process: comparing the demodulated I & Q output signals with the I & Q input signals, computing the
transfer curve, inverting this transfer curve, loading new coefficients from LUT (for non linearity signal
correction) and for ALE (linearity signal correction). The DAP output provides two parallel pre-
corrected I & Q digital signals.
In the TX card, these digital signals are then converted into the analogue domain and directly
transposed on a low-level RF signal. This unit also receives a sample of the output RF signal, which is
demodulated and split into two components, I & Q. These complex components are then digitised and
forwarded to DAP where they are compared with the input complex components. The TX card
performs an Automatic Level Control thanks to a detected envelope voltage from the power amplifier
channel of the transmitter.