TZA3034TTDH NXP Semiconductors, TZA3034TTDH Datasheet - Page 6

• Manufacturer Part Number: TZA3034TTDH
• Manufacturer: NXP Semiconductors

Specifications of TZA3034TTDH

• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 16
• Lead Free Status / RoHS Status: Not Compliant

Philips Semiconductors
more than a few millivolt should be avoided, since the
internal DC offset compensation circuit has a limited
correction range.
If AC coupling is used to remove any DC compatibility
requirement, the coupling capacitors must be large
enough to pass the lowest input frequency of interest.
For example, 1 nF coupling capacitors react with the
internal 4.5 k input bias resistors to yield a lower 3 dB
frequency of 35 kHz. This then sets a limit on the
maximum number of consecutive pulses that can be
sensed accurately at the system data rate. Capacitor
tolerance and resistor variation must be included for an
accurate calculation.
DC-offset compensation
A control loop connected between the inputs of buffer A3
and amplifier A1 (see Fig.1) will keep the input of buffer A3
at its toggle point in the absence of any input signal.
Because of the active offset compensation which is
integrated in the TZA3034, no external capacitor is
required. The loop time constant determines the lower
cut-off frequency of the amplifier chain, which is set at
approximately 850 Hz.
Input signal level-detection
The TZA3034 allows for user-programmable input signal
level-detection and can automatically disable the switching
of the PECL outputs if the input signal is below a set
threshold. This prevents the outputs from reacting to noise
in the absence of a valid input signal, and insures that data
will only be transmitted when the signal-to-noise ratio of
the input signal is sufficient for low bit-error-rate system
operation. Complementary PECL flags (ST and STQ)
indicate whether the input signal is above or below the
programmed threshold level.
The input signal is amplified and rectified before being
compared to a programmable threshold reference. A filter
is included to prevent noise spikes from triggering the
level-detector. This filter has a nominal 1 s time constant
and additional filtering can be achieved by using an
external capacitor between pin CF and V
driving impedance nominally is 25 k ). The resultant
signal is then compared to a threshold current through
pin RSET (see Fig.6). This current can be set by
connecting an external resistor R
pin RSET and V
The relationship between the threshold current and the
detected input voltage is approximately:
1998 Jul 07
I
RSET
SDH/SONET STM1/OC3 postamplifiers
=
0.002
CCA
V
, or by forcing a current into pin RSET.
DIN
–
V
DINQ
DETECT
A
between
CCA
(the internal
(1)
6
Since the voltage on pin RSET is held constant at 1.5 V
below V
Combining these two formulas results in a general formula
to calculate R
level-detection:
In this formula, V
Example: Detection should occur if the differential voltage
of the input signals drops below 4 mV (p-p). In this case, a
reference current of 0.002
pin RSET. This can be set using a current source or simply
by connecting a resistor of the appropriate value.
The resistor must be connected between V
pin RSET. In this example the resistor would be:
The hysteresis is fixed internally at 3 dB electrical. In the
example of above, a differential level below 4 mV (p-p) of
the input signal will drive pin ST to LOW, and an input
signal level above 5.7 mV (p-p) will drive pin ST to HIGH.
Since a JAM function is provided which forces the data
outputs to a predetermined state (DOUT = LOW and
DOUTQ = HIGH), the pins STQ and JAM can be
connected to automatically disable the signal transmission
when the chip senses that the input signal is below the
programmed threshold.
Response time of the input signal level-detection circuit is
determined by the time constant of the input capacitors,
together with the filter time constant (1 s internal plus the
additional capacitor at pin CF).
PECL output circuits
The output circuit of ST and STQ is given in Fig.7.
The output circuit of DOUT and DOUTQ is given in Fig.8.
Some PECL termination schemes are given in Fig.9.
I
R
R
RSET
DETECT
DETECT
=
CCA
----------------------- - A
R
=
=
DETECT
, the current flowing into this pin will be:
----------------------------------------- -
1.5
---------------- -
0.004
DETECT
V
750
DIN
DIN
750
–
and V
V
=
for a given input signal
TZA3034T; TZA3034U
DINQ
187.5 k
DINQ
0.004 = 8 A should flow into
are in V (p-p).
Objective specification
CCA
and
(2)
(3)