tza3012ahw NXP Semiconductors, tza3012ahw Datasheet - Page 8

• Manufacturer Part Number: tza3012ahw
• Description: 30 Mbits/s Up To 3.2 Gbits/s A-ratetm Fibre Optic Receiver
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Table 5 Channel selection
Both limiters can be made active by setting bit BOTHON in
I
where the second channel can be selected quickly if the
first channel loses its signal. Note that even when both
limiters are active, only one channel is selected at any
time; see Table 6.
When only one limiter is active, the time taken to
deactivate its limiter and activate the limiter in the other
channel takes 4 s typical.
Table 6 Channel and limiter selection with bit BOTHON
2003 May 21
2
handbook, halfpage
BOTHON
C-bus register LIMCNF. This allows ‘hot switching’,
I2CINSEL
I
30 Mbits/s up to 3.2 Gbits/s
A-rate
2
Fig.3
C BIT
0
1
0
1
0
0
1
1
I
2
C BIT
Limiter input termination configuration.
INSEL
IN
INQ
HIGH channel 1;
HIGH channel 1;
LOW
LOW
PIN
INSEL
fibre optic receiver
X
X
0
1
V CCA
V EE
limiter 1 active
limiters 1 and 2
active
channel 2;
limiter 2 active
channel 2;
limiters 1 and 2
active
INSEL
HIGH channel 1; limiter 1 active
LOW
PIN
SELECTED
CHANNEL
X
X
channel 2; limiter 2 active
channel 2; limiter 2 active
channel 1; limiter 1 active
SELECTED CHANNEL
MDB385
50
50
IN1 and IN1Q
IN1 and IN1Q
IN2 and IN2Q
IN2 and IN2Q
SELECTED
INPUTS
8
Received Signal Strength Indicator (RSSI)
The strength of signal present at each RF input is
measured by a logarithmic detector and represented by an
analog voltage at pins RSSI1 and RSSI2 for channels 1
and 2, respectively. The RSSI has a sensitivity of
17 mV/dB typical for an input voltage swing V
5 mV to 500 mV; see Fig.4. RSSI output voltage V
be calculated using the following formula:
Both logarithmic detectors are always active to allow the
input with the strongest signal to be selected.
Loss Of Signal (LOS) indicator
In addition to the analog RSSI output, the TZA3012AHW
also provides a digital LOS indication output on pins LOS1
and LOS2. The RSSI level is internally compared with a
LOS threshold voltage level, which can be set either by an
external resistor connected to pins LOSTH1 and LOSTH2,
or by using an internal D/A converter. The method used is
determined by bit I2CREFLVL1 in I
register LIMLOS1CNF (address BDH) for channel 1, or
bit I2CREFLVL2 in I
(address BFH) for channel 2. Using the internal
D/A converter requires a value representing the threshold
voltage to be programmed into I
LIMLOS1TH (address BCH) or LIMLOS2TH
(address BEH). This allows separate LOS threshold levels
to be specified per channel.
If the received signal strength is below the default
hysteresis value of 3 dB, the corresponding LOS pin will
be HIGH. Alternative hysteresis values from 0 to 7 dB in
steps of 1 dB can be specified using bits HYS1 and HYS2
in I
respectively. If required, the polarity of the LOS indicator
outputs can be inverted by setting bits LOS1POL
and LOS2POL in the same registers. The LOS function
can be disabled by setting bit LOS1 or LOS2 to logic 0 for
channel 1 or channel 2 respectively.
The LOS function is also available using I
INTERRUPT and STATUS; see Sections “Interrupt
register” and “Status register”. If bit LOS1 or LOS2 in
register INTERRUPT is not masked, a loss of signal
condition will generate an interrupt signal at pin LOS1 or
pin LOS2. Bits LOS1 and LOS2 are masked by default;
see Section “Interrupt generation”.
V
RSSI
2
C-bus registers LIMLOS1CNF and LIMLOS2CNF
=
V
RSSI(32 mV)
2
C-bus register LIMLOS2CNF
+
S
RSSI
20log
2
C-bus registers
TZA3012AHW
2
C-bus
Product specification
---------------- -
32 mV
V
i(p-p)
2
C-bus registers
i(p-p)
range of
RSSI
can