An integrated circuit including functional circuitry; test circuitry connected to the functional circuitry, wherein the test circuitry is arranged to control the testing of the functional circuitry; and clock signal generating circuitry connected to both the functional circuitry and the test circuitry. The communication apparatus includes a wireless transceiver and a computer readable storage medium. for an erbium-doped fiber amplifier or a Raman amplifier. Afterward, a gas pressure of at least 20 bar is produced in the pressure chamber outside the gas-tight region.