STDVE003A_08 Datasheet, PDF (11/41 Pages) STMicroelectronics – Adaptive 3.4 Gbps 3:1 TMDS/HDMI signal equalizer

STDVE003A
Figure 6. STDVE003A gain vs. frequency
Functional description
The STDVE003A equalizer is fully adaptive and automatic in function. The default setting of
EQ_BOOST = L is recommended for optimal operation. The equalizer’s performance is
optimized for all frequencies over the cable lengths from 1 m to 25 m at EQ_BOOST = L.
If cable lengths greater than 25 m are desired in application, then EQ_BOOST = H setting is
recommended.
Input termination
The STDVE003A integrates precise 50 Ω ± 5% termination resistors, pulled up to V_CC, on all
its differential input channels. External terminations are not required. This gives better
performance and also minimizes the PCB board space. These on-chip termination resistors
should match the differential characteristic impedance of the transmission line. Since the
output driver consists of current steering devices, an output voltage is not generated without
a termination resistor. Output voltage levels are dependent on the value of the total
termination resistance. The STDVE003A produces TMDS output levels for point-to-point
links that are doubly terminated (100 Ω at each end). With the typical 10 mA output current,
the STDVE003A produces an output voltage of 3.3 – 0.5 V = 2.8 V when driving a
termination line terminated at each end. The input terminations are selectable thus saving
power for the unselected ports.
Output buffers
Each differential output of the STDVE003A drives external 50 Ω load (pull-up resistor) and
conforms to the TMDS voltage standard. The output drivers consist of 10 mA differential
current-steering devices.
The driver outputs are short-circuit current limited and are high-impedance to ground when
OE_N = H or the device is not powered. The current steering architecture requires a
resistive load to terminate the signal to complete the transmission loop from V_CC to GND
through the termination resistor. Because the device switches the direction of the current
flow and not voltage levels, the output voltage swing is determined by V_CC minus the voltage
drop across the termination resistor. The output current drivers are controlled by the OE_N
pin and are turned off when OE_N is a high. A stable 10 mA current is derived by accurate
internal current mirrors of a stable reference current which is generated by band-gap voltage
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