TZA3033T/C3,112 NXP Semiconductors, TZA3033T/C3,112 Datasheet - Page 7

• Manufacturer Part Number: TZA3033T/C3,112
• Manufacturer: NXP Semiconductors

Specifications of TZA3033T/C3,112

• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 8
• Lead Free Status / RoHS Status: Compliant

Philips Semiconductors
AGC
The TZA3033 transimpedance amplifier can handle input
currents from 0.25 A to 1.6 mA. This means a dynamic
range of 79 dB. At low input currents, the transimpedance
must be high to obtain an adequate output voltage, and the
noise should be suitably low to guarantee minimum bit
error rate. At high input currents however, the
transimpedance should be low to avoid pulse width
distortion. This means that the gain of the amplifier has to
vary depending on the input signal level to handle such a
wide dynamic range. This is achieved in the TZA3033 by
implementing an Automatic Gain Control (AGC) loop.
The AGC loop consists of a peak detector, a hold capacitor
and a gain control circuit. The peak amplitude of the signal
is detected by the peak detector and stored on the hold
capacitor. The voltage across the hold capacitor is
compared to a threshold level. The threshold level is set at
an input current of 2.5 A (p-p). AGC becomes active only
for input signals larger than the threshold level. It is
disabled for smaller signals. The transimpedance is then
at its maximum value (44 k differential).
2002 Sep 06
SDH/SONET STM1/OC3
transimpedance amplifier
(1) V
(2) V
(3) V
handbook, full pagewidth
V o(dif)
(V)
V o
(mV)
CC
CC
CC
2.05
1.95
1.85
1.75
1.65
300
200
100
= 3.0 V.
= 3.3 V.
= 5.0 V.
0
10
1
1
Fig.6 AGC characteristics.
10
7
When the AGC is active, the feedback resistance of the
transimpedance amplifier is reduced to keep the output
voltage constant. The transimpedance is regulated from
44 k at low currents (I < 2.5 A) to 200
(I < 500 A). Above 500 A the transimpedance is at its
minimum and can not be reduced further but the front-end
remains linear until input currents of 1.6 mA (p-p).
The upper graph of Fig.6 shows the output voltages V
and V
current for a supply voltage of 3 V. In the lower graph the
difference between both output voltages, V
for supply voltages of 3, 3.3 and 5 V. It can seen from the
graph that the output changes linearly up to an input
current of 2.5 A where the AGC becomes active. From
this point on, the AGC tries to keep the differential output
voltage constant around 110 mV for medium range input
currents (input currents < 200 A). The AGC can not
regulate for input currents above 500 A, and the output
voltage rises again with the input current.
OUTQ
10
of the TZA3033 as a function of the DC input
2
(1)
10
3
(2)
(3)
Product specification
V OUT
V CC = 3 V
V OUTQ
I i ( A)
TZA3033
at high currents
o(dif)
MGT562
, is shown
10
4
OUT