tza3013bu-n3 NXP Semiconductors, tza3013bu-n3 Datasheet - Page 7

• Manufacturer Part Number: tza3013bu-n3
• Description: Sdh/sonet Stm16/oc48 Transimpedance Amplifier
• Manufacturer: NXP Semiconductors

Philips Semiconductors
AGC
The TZA3013 transimpedance amplifier can handle input
currents from 6 A to 1.7 mA which is equivalent to a
dynamic range of 49 dB. At low input currents, the
transimpedance must be high to obtain enough output
voltage, and the noise should be low enough to guarantee
a minimum bit error rate. At high input currents however,
the transimpedance should be low to avoid pulse width
distortion. To achieve the wide dynamic range requires the
gain of the amplifier to depend on the level of the input
signal. This is achieved in the TZA3013 by an AGC loop.
The AGC loop comprises a peak detector, a hold capacitor
and a gain control circuit. The peak detector detects the
amplitude of the signal and the hold capacitor stores it. The
hold capacitor voltage is compared to a threshold voltage
which corresponds to an input current of 50 A (p-p). The
AGC is only active when the input signal level is larger than
the threshold level and is inactive when the input signal is
smaller than the threshold level.
2001 Feb 26
handbook, full pagewidth
SDH/SONET STM16/OC48
transimpedance amplifier
V
V o(dif)
o(dif)
(mV)
V o
(V)
300
200
100
= V
3.2
3.1
3.0
2.9
2.8
0
OUT
1
V
OUTQ
10
Fig.7 AGC characteristics.
7
10
When the AGC is inactive, the transimpedance is at its
maximum value of 4 k differential. When the AGC is
active, the feedback resistor value of the transimpedance
amplifier is reduced, reducing its transimpedance, to keep
the output voltage constant. The transimpedance is
regulated from 4 k at low currents (I
high currents (I
remain linear over the whole input current range compared
to other configurations which clip the large signals, such as
those using Schottky diodes, for example.
The top half of Fig.7 shows the output voltage at pads OUT
and OUTQ (V
current (I
Fig.7 shows the difference between V
output voltage changes linearly up to an input current of
50 A. At this point and above, the AGC becomes active
and tries to keep the differential output voltage constant,
which is about 220 mV for a large range input current of
<1.7 mA.
2
I
) at a supply voltage of 3.3 V. The bottom half of
OUT
i
= 1.7mA). The AGC allows the amplifier to
and V
TZA3013A; TZA3013B
10
OUTQ
3
) as a function of DC input
V CC = 3.3 V
V OUT
I i ( A)
V OUTQ
Product specification
i
OUT
< 50 A) to 80
and V
MGT104
OUTQ
10
4
. The
at