CLOCK GENERATION CIRCUIT

摘要

A clock generation circuit comprises an internal clock signal source providing an internal clock signal (CLKJNT) and a synchronization device for synchronization the internal clock signal (CLKJNT) with a reference clock signal (CLK_REF) provided externally from the clock generation circuit. The synchronization device comprises n delay locked loop circuits (Sync_DLL_0, Sync_DLL_1, Sync_DLL_2, Sync_DLL_3), n being an integer greater than 1, each delay locked loop circuit (Sync_DLL_0, Sync_DLL_1, Sync_DLL_2, Sync_DLL_3) having a clock input for receiving the internal clock signal (CLKJNT) and a clock output for providing an output clock signal (CLK(0), CLK(1), CLK(2), CLK(3)) with an individual phase shift that is adjustable. The synchronization device further comprises a multiplexer (CLKMUX) having n inputs and an output wherein each of the n inputs is connected to an output of one of the n delay locked loops (Sync_DLL_0, Sync_DLL_1, Sync_DLL_2, Sync_DLL_3) and a control circuit. The control circuit is adapted to adjust at least one of the delay locked loop circuits (Sync_DLL_0, Sync_DLL_1, Sync_DLL_2, Sync_DLL_3) for providing an individual phase shift according to a current phase shift and to select that input of the multiplexer (CLKMUX) that receives an output clock signal (CLK(0), CLK(1), CLK(2), CLK(3)) of the adjusted delay locked loop circuit (Sync_DLL_0, Sync_DLL_1, Sync_DLL_2, Sync_DLL_3) that is synchronized in frequency and phase with the reference clock signal (CLK_REF), wherein the output of the multiplexer (CLKMUX) provides that output clock signal as synchronized clock signal (CLK_SYNC), and wherein the control circuit is adapted to toggle between the n delay locked loop circuits (Sync_DLL_0, Sync_DLL_1, Sync_DLL_2, Sync_DLL_3), in a way that the phase of the internal clock signal (CLKJNT) is successively shifted according to the current phase shift between the internal clock signal (CLKJNT) and the reference clock signal (CLK_REF).