Datasheet

ADN8102
Rev. B | Page 21 of 36
TRANSMITTERS
Output Structure and Output Levels
The ADN8102 transmitter outputs incorporate 50 Ω termina-
tion resistors, ESD protection, and an output current switch. Each
port provides control of both the absolute output level and the
pre-emphasis output level. It should be noted that the choice of
output level affects the output common-mode level. A 600 mV
peak-to-peak differential output level with full pre-emphasis
range requires an output termination voltage of 2.5 V or greater
(V
TTO
, V
CC
≥ 2.5 V).
V
CC
V
TTO
OP
ON
V
EE
Tx SIMPLIFIED DIAGRAM
Q1
Q2
I
TOT
RN
50Ω
RP
50Ω
ON-CHIP
TERMINATION
V3
VC
V2
VP
V1
VN
I
DC
+ I
PE
07060-006
ESD
Figure 41. Simplified Output Structure
Pre-Emphasis
The total output amplitude and pre-emphasis setting space is
reduced to a single map of basic settings that provide seven
settings of output equalization to ease programming for typical
channels. The PE_A/PE_B[1:0] pins provide selections 0, 2, 4,
and 6 of the seven pre-emphasis settings through toggle pin
control, covering the entire range of settings at lower resolution.
The full resolution of seven settings is available through the I
2
C
interface by writing to Bits[2:0] (PE[2:0] of the OUT_A/OUT_B
configuration registers) with I
2
C settings overriding the toggle
pin control. Similar to the receiver settings, the ADN8102 allows
joint control of all four channels in a transmit port. Table 15
summarizes the absolute output level, pre-emphasis level, and
high frequency boost for each of the basic control settings and
the typical length of the CX4 cable and FR4 trace that each
setting compensates.
Full control of the transmit output levels is available through the
I
2
C control interface. This full control is achieved by writing to
the OUT_A/OUT_B Output Level Control[1:0] registers for the
channel of interest. Table 17 shows the supported output level
settings of the OUT_A/OUT_B Output Level Control[1:0]
registers. Register settings not listed in Table 17 are not
supported by the ADN8102.
The output equalization is optimized for less than 1.75 Gbps
operation but can be optimized for higher speed applications at
up to 3.75 Gbps through the I
2
C control interface by writing to
the DATA RATE bit (Bit 4) of the OUT_A/OUT_B configuration
registers, with high representing 3.75 Gbps and low representing
1.75 Gbps. The PE CTL SRC bit (Bit 7) in the OUT_A/OUT_B
Output Level Control 1 register determines whether the pre-
emphasis and output current controls for the channel of interest
are selected from the optimized map or directly from the OUT_A/
OUT_B Output Level Control[1:0] registers (per channel). Setting
this bit high selects pre-emphasis control directly from the
OUT_A/OUT_B Output Level Control[1:0] registers, and setting
it low selects pre-emphasis control from the optimized map.
Table 14. Data Rate Select
OUT_A/OUT_B Configuration Bit 4 Supported Data Rates
0 (default) 0 Gbps to 1.75 Gbps
1 1.75 Gbps to 3.75 Gbps
Table 15. Transmit Pre-Emphasis Boost and Overshoot vs. Setting
PE[2:0] Register PE[1:0] Pins Boost (dB) Overshoot (%)
DC Swing
(mV p-p diff)
Typical CX4 Cable
Length (Meters)
Typical FR4 Trace
Length (Inches)
0 0 0 0 800 0 to 2.5 0 to 5
1 Not applicable 2 25 800 2.5 to 5 0 to 5
2 1 3.5 50 800 5 to 7.5 10 to 15
3 Not applicable 4.9 75 800 7.5 to 10 10 to 15
4 2 6 100 800 10 to 12.5 15 to 20
5 Not applicable 7.4 133 600 15 to 17.5 20 to 25
6 4 9.5 200 400 20 to 22.5 25 to 30
Table 16. Output Configuration Registers
Name Address Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default
OUT_A/OUT_B configuration 0xC0, 0xE0 EN DATA RATE PE[2] PE[1] PE[0] 0x20
OUT_A/OUT_B Output Level Control 1 0xC1, 0xE1 PE CTL SRC OUTx_OLEV1[6:0] 0x40
OUT_A/OUT_B Output Level Control 0 0xC2, 0xE2 OUTx_OLEV0[6:0] 0x40