78Q8392L Teridian Semiconductor Corp. (TDK Semiconductor), 78Q8392L Datasheet - Page 2

• Manufacturer Part Number: 78Q8392L
• Description: 10/100 Ethernet PHYS
• Manufacturer: Teridian Semiconductor Corp. (TDK Semiconductor)

Low Power Ethernet
Coaxial Transceiver
FUNCTIONAL DESCRIPTION
The 78Q8392L incorporates six basic functions of
the
transmitting, collision signaling, collision detection,
jabber timing, and the heartbeat function. Refer to
Figure 1 for a general system block diagram.
RECEIVER FUNCTIONS
The receiver senses signals through the RXI input,
which minimizes reflections on the transmission
media using a low capacitance, high resistance input
buffer amplifier. The CDS ground input attaches
directly to the input buffer from the coaxial shield to
eliminate ground loop noise.
In addition to the input buffer, the receiver data path
consists of an equalizer, data slicer, receiver squelch
circuitry, and an output line driver.
The equalizer improves the cable-induced jitter; the
data slicer restores equalized received signals to fast
transition signals with binary levels to drive the
receiver line driver; and the receiver line driver drives
the AUI cable through an isolation transformer that
connects to the AUI interface.
Noise on the transmission media is rejected by the
receiver squelch circuitry, which determines valid
data via three criteria: Average DC level, pulse width
and transition period. The DC voltage level is
detected and compared to a set level in the receiver
comparator circuit. The pulse width must be greater
than 20 ns to pass the narrow pulse filter; the
transition timer outputs a true level on the RX Data
Valid line provided the time between transitions is
less than about 200 ns. As long as a valid RXI signal
is detected, the output line driver remains enabled.
The transition timer disables the line driver when
there are no further transitions on the data medium,
and the RX+, RX- pins go to a zero differential
voltage state (Figure 3).
TRANSMITTER FUNCTIONS
The transmitter data path consists of a transmit input
buffer, pulse-shaping filter, transmit
circuitry and transmit output line driver. The
self-biasing transmit input buffer receives data
through an isolation transformer and translates the
AUI differential analog signal to square pulse
suitable for driving the pulse shaping filter.
Ethernet
Transceiver,
including
receiving,
squelch
2
The filter outputs a correctly shaped and bandlimited
signal to the transmit output driver, which drives the
transmission medium through a high impedance
current source. When the transmitter is off, the
capacitance of the transmit driver is isolated from the
transmission media by an external diode with a low
capacitance node. The shield of the transmission
media serves as the ground return for the transmitter
function.
A transmit squelch circuit, which consists of a pulse
threshold detector, a pulse width detector, and a
pulse duration timer, is used to suppress noise, as
well as crosstalk on the AUI cable. The squelch
circuitry disables the transmit driver if the signal at
TX+ or TX- is smaller than the pulse threshold. Pulse
noise is rejected by a pulse width detector that
passes only pulses with durations greater than 20
ns. The pulse duration timer disables the transmit
driver if no pulses are received for two-bit periods
following valid pulses. At the end of a transmission,
the pulse duration timer disables the transmitter and
triggers the blanking timer, used to block “dribble”
bits.
COLLISION DETECTION
A collision occurs when two or more transmitters
simultaneously transmit on the transmission media.
A collision is detected by comparing the average DC
level of the transmission media to a collision
threshold. The received signal at RXI is buffered and
sent through a low pass filter, then compared in the
collision threshold circuit. If the average DC level
exceeds a collision threshold, a 10 MHz signal is
output on the CD± pins.
COLLISION SIGNALING
When collision signaling is enabled, a 10 MHz signal
is sent from the CD± pins through an isolation
transformer to the DTE. When the function is
disabled, this output goes to a zero differential state.
The 10 MHz output from the CD pins indicates a
collision on the transmission media, a heartbeat
function, or that the transmitter is in jabber mode.