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[Studies in Computational Intelligence 481] Artur Babiarz, Robert Bieda, Karol Jędrasiak, Aleksander Nawrat (auth.), Aleksander Nawrat, Zygmunt Kuś (eds.) - Vision Based Systemsfor UAV Applications (2013, Sprin

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Omnidirectional Video Acquisition Device (OVAD) 129<br />

4.3 Offset Recovery System<br />

Amplifier output voltage can reach voltage which ranges between 0 and 3.3 [V],<br />

which is supply voltage of multiplex<strong>in</strong>g unit, when amplifier becomes saturated.<br />

Each <strong>in</strong>put of multiplex<strong>in</strong>g unit is hav<strong>in</strong>g its offset elim<strong>in</strong>ated by <strong>in</strong>put and output<br />

capacitor. This means that 1Vp-p video signal can oscillate between -0.5 [V] and<br />

0.5 [V]. Because of its supply voltage amplifiers could not amplify negative voltages<br />

and thus output signal would be damaged. That problem would not occur<br />

when <strong>in</strong>put voltage would take values between 0 [V] and 1.65 [V], because <strong>in</strong> that<br />

situation amplified output voltage (consider<strong>in</strong>g amplifiers ga<strong>in</strong> G = 2) would take<br />

values from 0 [V] to 3.3 [V] range. Applied solution is offset recovery system<br />

(fig. 6).<br />

Fig. 6. Offset recovery system [2]<br />

When, after offset elim<strong>in</strong>ation, signal voltage ranges from -0.5 [V] to 0.5 [V],<br />

capacitor is charged to V d level by diode, because there exists difference <strong>in</strong> voltage<br />

between signal and V d and diode BAT54A is connected <strong>in</strong> forward direction.<br />

When <strong>in</strong>put signal turns positive, capacitor is still charged to V d level and this<br />

means that <strong>in</strong>put voltage will add to the current one. Diode is now connected <strong>in</strong><br />

reverse direction because capacitor voltage is higher than V d . If signal turns aga<strong>in</strong><br />

to negative value capacitor will have lower voltage value than V d and will be<br />

charged aga<strong>in</strong>. In conclusion, signal will have its offset recovered and its value<br />

will be equal to V d -U d , where U d is value of diode voltage drop.<br />

4.4 Active Branch of Multiplex<strong>in</strong>g Unit<br />

Enabled branch of multiplex<strong>in</strong>g unit, when specified <strong>in</strong>put signal is chosen by<br />

multiplexer and forwarded to transmitter, is presented <strong>in</strong> fig. 7.

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