tza3019 NXP Semiconductors, tza3019 Datasheet - Page 13

• Manufacturer Part Number: tza3019
• Description: 2.5 Gbits/s Dual Postamplifier With Level Detectors And 2 X 2 Switch
• Manufacturer: NXP Semiconductors

Philips Semiconductors
RSSI and LOS detection
The TZA3019 allows AC-signal level detection. This can
prevent the outputs from reacting to noise during the
absence of a valid input signal, and can insure that data
only will be transmitted when the signal-to-noise ratio of
the input signal is sufficient to insure low bit error rate
system operation.
The RSSI detection circuit uses seven limiting amplifiers in
a ‘successive detection’ topology to closely approximate
logarithmic response over a total range of 70 dB. The
detectors provide full-wave rectification of the AC signals
presented at each previous amplifier stage. Their outputs
are current drivers. Each cell incorporates a low-pass filter,
being the first step in recovering the average value of the
demodulated signal of the input frequency. The summed
detector output currents are converted to a voltage by an
internal load resistor. This voltage is buffered and
available in the A and B versions of the TZA3019. When
V
prevent the LOS comparator from switching to the standby
mode. The LOS comparator detects an input signal above
a fixed threshold, resulting in a LOW-level at the LOS
circuit output.The threshold level is determined by the
voltage on pins LOSTH1 or LOSTH2 (see Fig.10). A filter
with a time constant of 1 s nominal is included to prevent
noise spikes from triggering the level detector.
The comparator (with internal 3 dB hysteresis) drives an
open-drain circuit with an internal resistor (5 k ) for direct
interfacing to positive or negative logic (see Fig.11). Only
available in the B and C versions of the TZA3019.
The response is independent of the sign of the input signal
because of the particular way the circuit has been built.
This is part of the demodulating nature of the detector,
which results in an alternating input voltage being
transformed to a rectified and filtered quasi DC-output
signal. For the TZA3019 the logarithmic voltage slope is
supply independent through four feedback loops in the
reference circuit. The internal LOS detector output voltage
is based on V
on the waveform and the response depends roughly on
the input signal RMS value. This influences high
frequencies, a square wave input of 2.4 GHz (LOS circuit
bandwidth of 2.4 GHz) offsets the intercept voltage by
20%. V
formula:
V
2001 Jun 25
V
RSSI
LOSTH
= 1/12.5 dB/mV and is essentially temperature and
CC
2.5 Gbits/s dual postamplifier with level
detectors and 2
+
is used V
0.458 S
LOSTH
= V
RSSI
–
ref
can be calculated using the following
LOSTH
. The demodulator characteristic depends
=
RSSI
must not be connected to GND to
20 log
2 switch
------------------- -
26E 8
V
i(p-p)
–
(1)
13
ndbook, halfpage
where S
Example: a 200 mV (p-p) single-ended 1.2 GB/s PRBS
signal has an V
A full understanding of the offset control loop is useful. The
primary purpose of the loop is to extend the lower end of
the dynamic range in any case where the offset voltage of
the first stage might be high enough to cause later stages
to prematurely enter limiting, caused by the high DC-gain
of the amplifier system. The offset is automatically and
continuously compensated via 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. Consequently, with DC-coupling, signal absence,
either LOW-level or HIGH-level is detected as a full signal,
only signals with an average value equal to zero give zero
output. Version B can be used for an auto function, which
switches the strongest input signal to output 1 and the
weakest to output 2. To achieve this output V
used as the reference voltage for input V
output LOS1 can switch S1 and S2.
V i(se)(p-p)
(1) PRBS pattern input signal with a frequency <1 GHz.
(2) Linearity error typically 0.5 dB.
(3)
(mV)
V CC 0.16
10
10
10
= 1/12.5 dB/mV.
RSSI
10
1
3
2
1
10
Fig.10 Loss of signal assert level.
= sensitivity (see Chapter “Characteristics”).
RSSI
20
LOW-level
LOS1,
LOS2
V CC 0.48
of V
V LOSTH1 , V LOSTH2 (% of V ref )
30
(3)
CC
40
1.013 V.
V CC 0.8
HIGH-level
(1)
(2)
LOS1,
LOS2
V RSSI1 , V RSSI2 (V)
50
Product specification
60
LOSTH
TZA3019
V CC 1.12
MGS564
RSSI2
70
. Then the
must be