ATA01504D1C Ver la hoja de datos (PDF) - ANADIGICS
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ATA01504D1C Datasheet PDF : 8 Pages
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ATA01504
Indirect Measurement of Optical Overload
Optical overload can be defined as the maximum
optical power above which the BER (bit error rate)
increases beyond 1 error in 1010 bits. The
ATA01504D1C is 100% tested at die sort by a DC
measurement which has excellent correlation with
an PRBS optical overload measurement. The
measurement consists of sinking a negative current
(see VOUT Vs IIN figure) from the TIA and determining
the point of output voltage collapse. Also the input
node virtual ground during heavy AGC is checked
to verify that the linearity (i.e. pulse width distortion)
of the amplifier has not been compromised.
Phase response
At frequencies below the 3dB bandwidth of the device,
the transimpedance phase response is
characteristic of a single pole transfer function (as
shown in the Phase Vs Frequency curve). The output
impedance is essentially resistive up to 1000 MHz.
Measurement of Input Referred Noise Current
The Input Noise Current is directly related to
sensitivity . It can be defined as the output noise
voltage (Vout), with no input signal, (including a 110
MHz lowpass filter at the output of the TIA) divided by
the AC transresistance.
14
Rf
10
CT
50
6
CT=1.0pF
Figure 9: Phase (IIN to VOUT)
2
CT =0.5pF
- 0.1
1
10
100 1000
Frequency (MHz)
Figure 8: Input Referred Noise Spectral Density
AGC Capacitor
It is important to select an external AGC capacitor of
high quality and appropriate size. The ATA01504D1C
has an on-chip 70 KW resistor with a shunt 4 pF
capacitor to ground. Without external capacitance the
chip will provide an AGC time constant of 280 nS. For
the best performance in a typical 155 MB/s SONET
receiver, a minimum AGC capacitor of 56pF is
recommended. This will provide the minimum
amount of protection against pattern sensitivity and
pulse width distortion on repetitive data sequences
during high average optical power conditions.
Conservative design practices should be followed
when selecting an AGC capacitor, since unit to unit
variability of the internal time constant and various
data conditions can lead to data errors if the chosen
value is too small.
6
PRELIMINARY DATA SHEET - Rev 1
08/2001
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