tza3014 NXP Semiconductors, tza3014 Datasheet - Page 11

• Manufacturer Part Number: tza3014
• Description: 2.5 Gbits/s Postamplifier With Level Detector
• Manufacturer: NXP Semiconductors

Philips Semiconductors
RSSI and LOS detection
The TZA3014 monitors the level of the input AC signal.
This function can prevent the output circuit from reacting to
noise in case there is no valid input signal, and can ensure
that only data is transmitted when there is sufficient input
signal for low bit error rate system operation.
The RSSI uses seven limiting amplifiers in a ‘successive
detection’ topology to closely approximate a logarithmic
response over a total range of 70 dB. The AC signal is
full-wave rectified by a detector at each amplifier stage.
Each detector output has a current driver followed by a
low-pass filter providing the first stage in the recovery of
the average value of the demodulated input signal. The
total current from each detector output is converted to a
voltage by an internal load resistor and then buffered.
When the RSSI output is used, input pin LOSTH is not to
be connected to GND (standby mode). The RSSI output
follows the internal 3 dB hysteresis of the LOS
comparator. The LOS comparator detects when the input
signal level rises above a programmable fixed threshold.
Then pin LOS gets a LOW-level. The threshold level is
determined by the voltage on pin LOSTH and by the level
of the input AC signal (see Fig.8). A filter with a nominal
time constant of 1 s prevents noise spikes from triggering
the level detector.
The LOS comparator has an internal 3 dB hysteresis and
drives an open-drain circuit with a 5 k internal resistor
allowing it to directly interface positive or negative logic
circuits (see Fig.9).
Its response is independent of the input signal polarity due
to the circuit design and to the demodulating action of the
detector which transforms the alternating input voltage to
a rectified and filtered quasi DC output signal. The
logarithmic voltage slope of the TZA3014 is
and supply voltage due to four feedback loops in the
reference circuit. The LOS detector output voltage is
derived from V
The sensitivity of the LOS detector is affected by the RMS
value of the input signal which, in its turn, depends on the
frequency.
V
V
where S
2001 Jun 25
V
LOSTH
LOSTH
=
CC
2.5 Gbits/s postamplifier with level detector
1
/
+
12.5
0.458 S
can be calculated using the following formula:
= V
RSSI
dB/mV and mostly is independent of temperature
RSSI
in [mV/dB]; V
–
ref
=
RSSI
.
20 log
LOSTH
------------------- -
26E 8
, V
V
i(p-p)
RSSI
–
and V
i(p-p)
in [V].
(1)
11
Example: a 200 mV (p-p) single-ended 1.2 GB/s PRBS
input signal will have a V
If the offset voltage of the first stage increases above a
certain level, the high DC gain of the amplifier circuit will
cause successive stages to limit prematurely. This is
prevented by the LOS detector offset control loop which
extends the lower end of the amplifier’s dynamic range.
The offset is automatically and continuously compensated
by a feedback path from the last stage. An offset at the
output of the logarithmic converter is equivalent to a
change of amplitude at the input.
Using DC-coupling, with signal absence, and V
to V
very small signals with an average value equal to zero, can
result into a zero output.
handbook, halfpage
(1) PRBS pattern input signal with a frequency <1 GHz.
(2) Linearity error typically 0.5 dB.
(3)
INQ
V i(se)(p-p)
(mute), the LOS detector detects full signal. Only
(mV)
=
1
V CC 0.16
10
/
12.5
10
10
10
Fig.8 Loss of signal assert level.
1
3
2
1
10
dB/mV.
20
LOW-level
LOS
V CC 0.48
RSSI
30
(3)
voltage of V
40
V LOSTH (% of V ref )
V CC 0.8
HIGH-level
(1)
(2)
Product specification
LOS
50
V RSSI (V)
TZA3014
CC
60
V CC 1.12
IN
1.013 V.
MGU129
not equal
70