tza3014 NXP Semiconductors, tza3014 Datasheet - Page 7

• Manufacturer Part Number: tza3014
• Description: 2.5 Gbits/s Postamplifier With Level Detector
• Manufacturer: NXP Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
The TZA3014 is a postamplifier with a RSSI circuit to
provide output signals for RSSI and LOS (see Fig.1). The
input signal can be amplified to a programmable level.
An active level control circuit ensures this level. The
control voltage on pin INV inverts the outputs, so avoiding
a required complicated Printed Circuit Board (PCB) layout.
An offset compensation circuit minimizes the effect of any
voltage offset present at the input.
The RSSI and LOS detector are based on a 7-stage
‘successive detection’ circuit which provides a logarithmic
output. The LOS detector is followed by a comparator with
a programmable threshold. The input signal level detection
is implemented to check if the input signal is above the
user-programmed level. The user can ensure that data will
only be transmitted when the input signal-to-noise ratio is
sufficient for low bit error rate system operation. A second
offset compensation circuit minimizes the effect of any
voltage offset present in the logarithmic amplifier.
RF input circuit
The input circuit contains internal 50
decoupled to V
capacitor (see Fig.4).
The inputs IN and INQ are DC-biased at approximately
V
TZA3014 can be DC-coupled, but AC coupling is
preferred. When DC-coupled, the drive source must
operate within the allowable input range
(V
should stay below a few millivolts since the internal
DC-offset compensation circuit has a limited correction
range. When AC-coupled, do not use capacitors that
cause a 3 dB cut-off point at 50 kHz (postamplifier cut-off
point) or at 1 MHz (RSSI cut-off point).
RF output circuit
Matching the outputs of the postamplifier (see Fig.5) is not
mandatory. In most applications, the receiving end of the
transmission line will be properly matched, causing very
few reflections.
Matching the transmitting end of the transmission line to
absorb reflections only, is recommended for very sensitive
applications.
In such cases, 100
connected to V
possible to the IC. However, for most applications these
matching resistors are not required.
2001 Jun 25
CCA
CCA
2.5 Gbits/s postamplifier with level detector
0.33 V by an internal reference generator. The
1.0 V to V
CCA
CCB
CCA
via an internal common mode 12 pF
and pins OUT and OUTQ as close as
pull-up resistors should be
+ 0.3 V). The DC-offset voltage
resistors
7
RF output level adjustment
The output level can be made compatible with CML or
PECL by adjusting the voltage on pin LEVEL. The
DC voltages on pins OUT and OUTQ relate to the
DC voltage on pin LEVEL. Due to the effect of the 50
load resistance at the receiving end, for a given
peak-to-peak value on pins OUT and OUTQ, a different
voltage is required on pin LEVEL in case the output is
AC-coupled and when the output is DC-coupled
(see Figs 5 and 6).
When pin LEVEL is not connected or connected to V
the postamplifier is in power-down state (see Fig.5).
DC-offset compensation loop
A DC-offset compensation loop connected between the
amplifier output and the buffer input maintains the toggle
point at the buffer input when there is no input signal
(see Fig.1). This active control circuit is integrated and
does not require an external capacitor. The loop
time constant determines the lower cut-off frequency of
the amplifier chain, and is internally fixed at approximately
5 kHz.
handbook, halfpage
INQ
IN
Fig.4 RF input circuit.
12 pF
50
420
50
Product specification
TZA3014
MGU125
V CCA
GNDA
CCA
,