TZA3023T NXP Semiconductors, TZA3023T Datasheet - Page 7

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TZA3023T

Manufacturer Part Number
TZA3023T
Description
Manufacturer
NXP Semiconductors
Datasheet

Specifications of TZA3023T

Operating Temperature (min)
-40C
Operating Temperature (max)
85C
Operating Temperature Classification
Industrial
Mounting
Surface Mount
Pin Count
8
Lead Free Status / RoHS Status
Not Compliant

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Company
Part Number
Manufacturer
Quantity
Price
Part Number:
TZA3023T
Manufacturer:
TAIYO
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Part Number:
TZA3023T
Manufacturer:
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Quantity:
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Philips Semiconductors
AGC
TZA3023 transimpedance amplifier can handle input
currents from 0.5 A to 1.5 mA. This means a dynamic
range of 72 dB. At low input currents, the transimpedance
must be high to get enough output voltage, and the noise
should be low enough to guaranty 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 TZA3023 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 it is stored on the hold
capacitor. The voltage over the hold capacitor is compared
to a threshold level. The threshold level is set to
10 A (p-p) input current. AGC becomes active only for
input signals larger than the threshold level.
2002 Sep 05
handbook, full pagewidth
SDH/SONET STM4/OC12
transimpedance amplifier
V
(1) V
(2) V
(3) V
V o(dif)
o(dif)
(mV)
V o
(V)
600
400
200
1.8
1.6
1.4
1.2
= V
CC
CC
CC
0
1
1
= 3 V.
= 3.3 V.
= 5 V.
OUT
V
OUTQ
.
10
Fig.7 AGC characteristics.
7
10
2
It is disabled for smaller signals. The transimpedance is
then at its maximum value (21 k differential).
When the AGC is active, the feedback resistor of the
transimpedance amplifier is reduced to keep the output
voltage constant. The transimpedance is regulated from
21 k at low currents (I < 10 A) to 800
(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 1.5 mA.
The upper part of Fig.7 shows the output voltages of the
TZA3023 (OUT and OUTQ) as a function of the DC input
current. In the lower part, the difference of both voltages is
shown. It can be seen from the figure that the output
changes linearly up to 10 A input current where AGC
becomes active. From this point on, AGC tries to keep the
differential output voltage constant around 200 mV for
medium range input currents (input currents <200 A).
The AGC can not regulate any more above 600 A input
current, and the output voltage rises again with the input
current.
(1)
(2)
(3)
10
3
V CC = 3 V
V OUT
V OUTQ
I i ( A)
Product specification
TZA3023
at high currents
MCD914
10
4

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