SL3522CMC MITEL [Mitel Networks Corporation], SL3522CMC Datasheet - Page 5

• Manufacturer Part Number: SL3522CMC
• Description: 500MHz 75dB Logarithmic/Limiting Amplifier
• Manufacturer: MITEL [Mitel Networks Corporation]

APPLICATION NOTES
1)
produce a trimmable Video transfer characteristic. Both the
gain (Slope) and Offset of the amplifier can be externally
adjusted.
a)
circuits in figs 5 and 6)
and R
difference from the Trim reference resistor, R
Gain has an effect on Offset, but adjustment of Offset does
NOT affect the Gain. Therefore the Gain should be optimised
first. The Offset should only be adjusted once the Gain has
been set.
for a fixed value of R
for a fixed value of R
compensation for Video gain (Slope). To ensure temperature
stability for Video gain (Slope) over the operating temperature
range, it is recommended that the resistors with identical
temperature coefficients of resistance are used for R
compensation for Video Offset. Although it is recommended
that a resistor with identical temperature coefficient of
resistance to R
additional external temperature compensating network.
b) Video performance
16ns (10% - 90%).In order to achieve this transient
performance, it is important to ensure that:-
nominal resistance of 1.5k , with a parasitic capacitance
LESS than 5pF.
exceed 200 resistance in parallel with 20pF.
a 10nF capacitor to the RETURN line from the video load,
connected to Video GND (pin 16), avoiding any common
impedance path.
with a 10nF capacitor DIRECTLY to Video-Output V
14).
2)
with RF output buffer disabled (pin 8 floating)
detection amplifier only, with no requirement for a limited RF
Output, the RF input (pins 27 and 28) can be driven EITHER
differentially or single ended from a 50 source. If being used
with a single ended input, the SIGNAL should be applied to pin
27 and the RETURN should be connected to pin 28, as shown
in the Application circuit diagram in Fig 5.
Although not a crucial requirement, it is recommended that the
device should be mounted using a ground plane.
VIDEO–AMPLIFIER
The SL3522 uses a single ended Video amplifier to
Gain and Offset trimming (ref Applications
The Gain and Offset control is achieved by adjusting R
Fig 7 shows the variation of Video Offset with value of R
Fig 8 shows the variation of Video Slope with value of R
The Video amplifier incorporates temperature
The Video amplifier does NOT incorporate temperature
The Video–amplifier has a critically damped rise time of
i) the resistor connected to Trim reference (pin 18), has a
ii) the load applied to the Video Output (pin 13) does NOT
Also, the following decoupling should be incorporated:-
i) The Video Output V
ii) The Video Output Vee (pin 12) should be decoupled
SL3522 AS A LOG AMPLIFIER
If the SL3522 is to be used as a Logarithmic successive
The SL3522 is VERY stable when used in this way.
O
respectively. The control is dependent upon their
T
be used for R
T
T
and R
and R
CC
(pin 14) should be decoupled with
G
O
O
= 1k5 .
= 1k5 .
, it may be necessary to use an
T
. Adjustment of
T
and R
CC
(pin
O
G
G
G
,
,
.
3) SL3522 AS A LOG/LIMITING AMPLIFIER
- with RF Output-Buffer ENABLED (pin 8 connected
to GND)
amplifier with a requirement for a Limited RF Output signal,care
is required in the layout of components and connections around
the device to ensure stability. The following precautions should
be observed (refer to Application circuit diagram in Fig. 6):-
ensuring that the impedance between the ground plane and
ALL the GND pins is kept as low as possible. If a multilayer PCB
is used where the ground plane is connected to the GND pins
using through-plated holes (vias), it is essential to ensure that
the vias have a very low impedance. ALL supply decoupling
capacitors should be RF chip capacitors whose leads should be
kept as short as possible.
should be connected to a low impedance copper plane. A two
layer PCB should help to achieve this.
balanced source impedance. One way of achieving this is to
use an isolating BALUN transformer (50 UNBALANCED
50
the RF input pins. (e.g. Mini circuits TT1–6, TO –75). The device
stability is VERY sensitive to an imbalance of the differential
source impedance at pins 27 and 28. Use of a transmission line
BALUN though, is NOT recommended.
be loaded with matched impedances ideally 50 transmission
lines. The RF Output lines leading away from the device should
be balanced. Driving highly reactive SWR loads is NOT
recommended as these can encourage device instability, as
can an imbalance of the differential load impedance at pins 9
and 10.
coupled, and ideally the output pins should be capacitively
coupled to their loads using 1nF capacitors. However the RF
Outputs can drive a DC load to GND and a DC offset of approx.
400mV will exist on each RF Output pin. IT WILL NOT BE
POSSIBLE TO DISABLE THE RF OUTPUT BUFFER UNDER
THESE CONDITIONS.
self noise, particularly at low ambient temperatures (-55 C),
when the RF output buffer is enabled.
NOTE that this will effect the liminting range as the gain of the
RF output buffer will reduce as the amount of noise limiting
increases.
an attenuation network as shown in fig. 9. Under these
conditions the effective RF Output currents will be reduced,
allowing the device to operate with a greater margin of
stability.It may be possible to run the device without a BALUN
transformer on the RF input if the total output impedance on the
RF Output >> 50
mounted as close as possible to the RF Output connections
(pins 9 and 10). The RF input connection could then be
configured as in Fig 5.
If the SL3522 is to be used as a Limiting or Log/limiting
a) The device should be mounted on a ground plane,
b) The RF V
c) The RF input (pins 27 and 28) should be driven with a
BALANCED) connected between the signal source and
d) The RF Output connections (pins 9 and 10) should each
e) The RF Output connections (pins 9 and 10) are DC
f) The RF output (pins 9 and 10) has a tendancy to limit on
If required the limited RF Output can be attenuated using
EE
connections (pins 3,5,7,11,20,22,24,26)
, and the attenuation components are
SL3522
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