CS6721 integrates three main functions in a single chip
providing optimal solutions for various fiber module
applications. The functional blocks include a 2.5G post-
amplifier, a 1.25G burst or continuous mode LD driver,
and an 8-bit MCU for configuring and controlling the
The post-amplifier receives AC coupled differential
signal from pre-amplifier and performs the quantization
amplifications. There are total four amplification stages
excluding the output stage. The offset cancellation is
built-in on chip. The LOS status is also configurable as a
set peak level detection by the post-amplifier or
combined with ADC detection on peak level.
The LD driver performs the transmit function that
receives the PECL differential signal TXINP/TXINN and
convert to drive LD output driver. The LD driver is also
controlled by burst-enable signal BENN/BENP. The
polarity of control can be configured. The laser driver
includes differential modulation outputs and DC bias
control output. The setting of output power level is
controlled through automatic power control loop and is
configurable by MCU. The output can be connected to
Laser diode either by AC or DC coupled. The transmit
path can be enabled or disabled by TXEN signal.
The on-chip MCU is the flexibility and versatility of
controlling and configurations of fiber module design.
Almost all configurations and parameters of the PA and
LD driver parameters and can be controlled by MCU
through software. The 12-bit ADC associated with MCU
can be used to acquire various internal and external
analog signals such on-chip temperature sensor and
reference voltages. The MCU has 2K boot ROM and 2K
SRAM for program storage which can meet the need of
application of SFP/PON, Also the boot ROM is
responsible for uploads the user program from external
serial EEPROM(with capacity of 2k 4k 8k), The I2C
slave interface also serves as ISP/IAP interface as well
as SFP/SFF DMI function.
CS6721 integrates essential building blocks for Fiber
module design. The integration of MCU allows precision
control to tailor various module applications and
facilitates configuration and automatic calibration in the
manufacturing process. Using CS6721, the module can
achieve low cost and high performance and can be
applied in FTTH, BPON, GEPON, and GPON.
SONET/SDH, FTTH, GEPON, GPON.