Functional description STA1102R
8/18 Doc ID 16470 Rev 5
3.3 Input termination
The STA1102R integrates precise 50 Ω ± 10% termination resistors, pulled up to V
Cm
, on all
its differential input channels. External terminations are not required. This gives improved
performance and also minimizes the PCB board space. These on-chip termination resistors
should match the differential characteristic impedance of the transmission line.
3.4 Low power modes
There are 2 types of low power modes in the STA1102R: hardware low and auto low power
modes.
3.4.1 Hardware low power mode
The EN input activates a hardware low power mode. There is an internal pull-up resistor to
maintain the EN in the default (HIGH) state. When this low power mode is activated
(EN = L), all input and output buffers and internal bias circuitry are powered off and disabled.
Outputs are driven to HiZ in low power mode. There is a delay associated with entering
(max. 2
µs) and exiting (max. 20 µs) this hardware low power mode.
3.4.2 Auto low power mode
The auto low power mode is activated when differential voltage at either or both of the
channels is < 50 mV for more than 3
µs. During this low power mode, output of the
associated channel is driven to V
cm
and the selective circuit block is disabled to lower power
consumption. The delay associated with exiting the auto low power mode is 50 ns max.
3.5 Squelch detector
A squelch detector is integrated on the input of each of the 2 data paths. The squelch
detector is a high-speed amplitude comparator that is turned on when EN = H. The
differential input signal is monitored by the detector. When the differential input is detected
to be less than or equal to 50 mV, the input signal is considered an invalid signal and is not
passed to the output. When this happens, the corresponding output is biased to V
CM
. When
the differential input is greater than or equal to 150 mV, the input signal is considered valid
signal and is passed to the output.
The integration of the squelch detector helps the system to prevent responding to noises.
As such, it enables the device to fully support OOB signaling.
Obsolete Product(s) - Obsolete Product(s)
