U.S. Philips Corporation

Holger Ernst

Holger Moll

In a frequency modulator (1) having an adjusting circuit by which frequency modulator an applied luminance signal of a color video signal that contains synchronization pulses is frequency modulated, while the chrominance signal of the color video signal is modulated on a carrier, that has a quiescent frequency if no color information is available. A capacitor is provided for an automatic mode of operation, and is charged or discharged, respectively, in dependence on the period duration of the modulator output signal and in dependence on the period duration of the quiescent frequency of the chrominance carrier. The steepness of the voltage/frequency characteristic curve of the modulator is set dependent upon the charge condition of the capacitor, while the charging-to-discharging ratio is selected such that the charge of the capacitor is maintained constant on average, if the modulator frequency is equal to a predefined nominal frequency and increases or decreases, respectively, if the modulator frequency falls short of or exceeds the nominal frequency during the synchronization pulses.

Frequency modulator comprising an adjusting circuit

Integrated circuits which process analog signals and consist of a plurality of separate functional blocks are difficult to test because the terminals of, internally interconnected functional blocks cannot be simply fed out in view of the limited number of external terminals. In order to test the integrated circuit by testing individual functional blocks separately, it is proposed to connect inputs and outputs of functional blocks are connected to switches enabling connection of these functional blocks to external terminals. The switches are controlled by storage stages which are loaded via a test input which is connected to comparators. These comparators compare the input signal with various reference voltages, the voltage ranges between the reference signals being associated with the logic values '0' and '1' as well as with a clock signal value. This enables a series of data with a data clock to be applied via only one test input in order to switch the internal switches in conformity with the desired test state.

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Hamburg, Germany

Holger Ernst