The sleep mode is used in idle time when there is no call going on. Between paging blocks the system just waits for next paging block and may as well go into sleep. In the sleep mode all RF blocks except VCTXCO are powered off to conserve power. In baseband, reduction in power consumption is achieved by using deep-power-down mode in the Flash memory and using the 32kHz sleep mode clock for clocking the system control ASIC.
The system control ASIC MAD2 may go into sleep mode with software control. SMART ASIC derives a 32 kHZ sleep clock from the 13MHz system clock. MAD2 uses this low-frequency clock in sleep mode to keep the system synchronized with network. The system clock can not be turned off because the SMART ASIC is using it for synchronizing the PCMCIA bus. Other sections in the RF block can be powered down. MAD2 controls the external power-down with its VCXOPwr -pin. Furthermore it puts the Flash memory in deep-power down mode.
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