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Lattice Semiconductor
ORCA ORSO42G5 and ORSO82G5 Data Sheet
21
The receiver section receives high-speed serial data at its differential CML input port. These data are fed to the
clock recovery section which generates a recovered clock and retimes the data. This means that the receive clocks
are asynchronous between channels. The retimed data are deserialized and presented as an 8-bit parallel data on
the output port. Two-phase receive byte clocks are available synchronous with the parallel words.
A fractional band-gap voltage generator is included on the design. An external resistor (3.32 kΩ ± 1%), connected
between the pins REXT and VSSREXT generates the bias currents within the chip. This resistor should be able to
handle at least 300 A.
32:8 MUX
The MUX block is responsible for converting 32 bits of data at 77.76 MHz to 8 bits of data at 311.04 MHz. It will
contain a small elastic store for clock domain transfer between the write clock from the FPGA to the divide-by-4
clock from the SERDES output clock (XCK311). It is recommended to use the clocking scheme shown later in
responsible for producing the divide-by-4 clock from the SERDES output clock (XCK311) which is 311.04 MHz at a
line rate of 2.488 Gbps.
In the MUX block 32-bit data synchronous to the 77.76 MHz is multiplexed to LDOUTx[7:0] synchronous to the
311.04 MHz SERDES output clock. Parallel 32-bit data can be received directly from the FPGA logic (SERDES
only mode) or from the payload sub-block. Bit and byte alignment for the MUX block is shown in
Figure 7.Figure 7. Bit and Byte Alignment for MUX Block
The serialized data are available at the differential CML outputs to drive either an optical transmitter, coaxial media,
or circuit board/backplane. The transmitter’s CML output buffer is terminated on-chip by 86Ω to optimize the data
eye as well as to reduce the number of discrete components required. The differential output swing reaches a max-
imum of 1.2 VPP in the normal amplitude mode. A half amplitude mode can be selected via conguration register bit
HAMP_xx. Half amplitude mode can be used to reduce power dissipation when the transmission medium has min-
imal attenuation or for testing of the integrity (loss) of the physical medium.
A programmable preemphasis circuit is provided to boost the high frequencies in the transmit data signal to maxi-
mize the data eye opening at the far-end receiver. Preemphasis is particularly useful when the data are transmitted
over backplanes or low-quality coax cables which have a frequency-dependent amplitude loss. For example, for
FR4 material at 2.5 GHz, the attenuation compared to the 1.0 GHz value is about 3 dB. The attenuation is a result
of skin effect loss of the PCB conductor and the dielectric loss of the PCB substrate. This attenuation causes inter-
symbol interface which results in the closing of the data eye at the receiver.
Time
W
O
R
D
3
W
O
R
D
2
W
O
R
D
1
W
O
R
D
0
32:8
MUX
W
0
W
1
W
2
W
3
Bit and Byte alignment of the
32-bit 77MHz data LDIN[0:7]
through the 32:8 MUX block
to LDIN[0:7 is shown in the
diagram to the left.
7
0
7
0
31
0