def display_window(self):
        """Read the channel name from QComboBox and plot its spectrum.

        This function is necessary it reads the data and it sends it to
        self.display. When the user selects a smaller chunk of data from the
        visible traces, then we don't need to call this function.
        """
        if self.idx_chan.count() == 0:
            self.update()

        chan_name = self.idx_chan.currentText()
        lg.debug('Power spectrum for channel ' + chan_name)

        if chan_name:
            trial = 0
            data = self.parent.traces.data(trial=trial, chan=chan_name)
            self.display(data)
        else:
            self.scene.clear()