TSH112 STMicroelectronics, TSH112 Datasheet - Page 14

• Manufacturer Part Number: TSH112
• Description: WIDE BAND, LOW NOISE OPERATIONAL AMPLIFIERS
• Manufacturer: STMicroelectronics

TSH110-TSH111-TSH112-TSH113-TSH114
Printed Circuit Board Layout Considerations
In this range of frequency, printed circuit board
parasitics can affect the closed-loop performance.
The implementation of a proper ground plane in
both sides of the PCB is mandatory to provide low
inductance and low resistance common return.
Most important for controlling the gain flatness
and the bandwidth are stray capacitances at the
output and inverting input. For minimizing the cou-
pling, the space between signal lines and ground
plane will be increased. Connections of the feed-
back components must be as short as possible on
order to decrease the associated inductance
which affect high frequency gain errors. It is very
important to choose external components as small
as possible such as surface mounted devices,
SMD, in order to minimize the size of all the dc and
ac connections.
Power Supply Bypassing
A proper power supply bypassing comes very im-
portant for optimizing the performance in high fre-
quency range. Bypass capacitors must be placed
as close as possible to the IC pins to improve high
frequency bypassing. A capacitor greater than
1 F is necessary to minimize the distortion. For a
better quality bypassing a capacitor of 0.1 F will
be added following the same condition of imple-
mentation. These bypass capacitors must be in-
corporated for the negative and the positive sup-
plies.
(fig.32):
Channel Separation or Crosstalk
The following figure show the crosstalk from an
amplifier to a second amplifier. This phenomenon,
accented in high frequencies, is unavoidable and
intrinsic of the circuit.
14/19
Circuit for power supply bypassing.
+
+
_
_
TSH11x
TSH11x
+V
+V
-V
-V
CC
CC
CC
CC
0.1 F
0.1 F
1 F
1 F
1 F
1 F
0.1 F
0.1 F
Nevertheless, the PCB layout has also an effect
on the crosstalk level. Capacitive coupling be-
tween signal wires, distance between critical sig-
nal nodes, power supply bypassing, are the most
significant points.
(fig.33):
A
Single Power Supply
The TSH11x operates from 12V down to 5V power
supplies. This is achieved with a dual power sup-
ply of ±6V and ±2.5V or a single power supply of
12V and 5V referenced to the ground. In the case
of this asymmetrical supplying, a biasing is neces-
sary to assume a positive output dynamic range
between 0V and +Vcc supply rails. Considering
the values of V
vide an ouput dynamic from +1.35V to 10.75V for
a 12V supplying, from 0.6V to 4.5V for a 5V sup-
plying.
The following figure show the case of a 5V single
power supply configuration.
(fig.34):
V
IN
IN
R1
R1
5k
5k
R1
R1
5k
5k
=+2, R
+5V
+5V
10 F
10 F
-100
-20
-40
-60
-80
0
10k
+ 1 F
+ 1 F
fb
Crosstalk vs. Frequency.
Circuit for +5V single supply.
Rin
Rin
1k
1k
=680 , C
10nF
10nF
100k
OH
+
+
fb
and V
R
R
680
680
=2pF, R
C
C
G
G
G
G
Frequency (Hz)
+
+
_
_
TSH11x
TSH11x
OL
1M
L
R
R
, the amplifier will pro-
+5V
+5V
=100 , Vcc=±6V, ±2.5V
fb,
fb,
C
C
2pF
2pF
680
680
fb
fb
100 F
100 F
10M
50
50
OUT
OUT
100M
50
50