Datasheet
20 _____________________________________________________________________________________
MAX3946
1Gbps to 11.3Gbps, SFP+ Laser Driver
with Laser Impedance Mismatch Tolerance
Bias Current Increment Setting Register (BIASINC)
Bit 7: SET_IBIAS[0]. This is the LSB of the SET_IBIAS[8:0] bits. This bit can only be updated by the use of BIASINC[4:0].
Bits 4 to 0: BIASINC[4:0]. This string of bits is used to increment or decrement the bias current. When written to, the
SET_IBIAS[8:0] bits are updated. BIASINC[4:0] are a two’s complement string.
Mode Control Register (MODECTRL)
Bits 7 to 0: MODECTRL[7:0]. The MODECTRL register enables the user to switch between normal and setup modes.
The setup mode is achieved by setting this register to H0x12. MODECTRL must be updated before each write opera-
tion. Exceptions are MODINC and BIASINC, which can be updated in normal mode.
Pulse-Width Control Register (SET_PWCTRL)
Bits 3 to 0: SET_PWCTRL[3:0]. This is a 4-bit register used to control the eye crossing by adjusting the pulse width.
Deemphasis Control Register (SET_TXDE)
Bits 5 to 0: SET_TXDE[5:0]. This is a 6-bit register used to control the amount of deemphasis on the transmitter output.
When calculating the total modulation current, the amount of deemphasis must be taken into account. The deemphasis
is set as a percentage of modulation current.
Equalization Control Register (SET_TXEQ)
Bits 2 to 1: SET_TXEQ[2:1]. These 2 bits are used to control the amount of equalization on the transmitter input. See
Table 1 for more information.
Bit #
7 6 5 4 3 2 1 0 ADDRESS
Name
SET_IBIAS
[0] (LSB)
X X
BIASINC
[4] (MSB)
BIASINC
[3]
BIASINC
[2]
BIASINC
[1]
BIASINC
[0] (LSB)
H0x0D
Default Value 0 0 0 0 0 0 0 0
Bit #
7 6 5 4 3 2 1 0 ADDRESS
Name
MODECTRL
[7] (MSB)
MODECTRL
[6]
MODECTRL
[5]
MODECTRL
[4]
MODECTRL
[3]
MODECTRL
[2]
MODECTRL
[1]
MODECTRL
[0] (LSB)
H0x0E
Default Value 0 0 0 0 0 0 0 0
Bit #
7 6 5 4 3 2 1 0 ADDRESS
Name X X X X
SET_PWCTRL
[3] (MSB)
SET_PWCTRL
[2]
SET_PWCTRL
[1]
SET_PWCTRL
[0] (LSB)
H0x0F
Default Value X X X X 0 0 0 0
Bit #
7 6 5 4 3 2 1 0 ADDRESS
Name X X
SET_TXDE
[5] (MSB)
SET_TXDE
[4]
SET_TXDE
[3]
SET_TXDE
[2]
SET_TXDE
[1]
SET_TXDE
[0] (LSB)
H0x10
Default Value X X 0 0 0 0 0 1
Bit #
7 6 5 4 3 2 1 0 ADDRESS
Name X X X X X
SET_TXEQ
[2]
SET_TXEQ
[1]
X
H0x11
Default Value X X X X X 0 0 X