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SMALL CIRCUITS
COLLECTION
006
Full-Duplex Data Transmission
K.J. Thiesler
+4V5...+16V
16mA
+4V5...+16V
16mA
The TH4062 is a dual video amplifier with
a 3-dB bandwidth of 180 MHz. This video
opamp also features low noise, a high
output current of
C11
C12
C21
C22
100 mA, a very high
slew rate, extremely low phase and gain
errors (0.02 ° and 0.02 %) and outstand-
ingly low crosstalk (–110 dB). These
properties make the TH4062 an excellent
choice for use in a high-speed data link.
The full-duplex capability supports bi-
directional communications (without a
changeover switch) for distances of up to
300 m using a coaxial or twisted-pair
cable.
The circuit diagram shows that all tha is
needed is four opamps (housed in two
ICs), a few resistors and some capaci-
tors to decouple the supply voltage. Two
independent PAL signals are fed into
inputs A
IN
and B
IN
. These signals appear
unchanged at the corresponding remote
outputs A
OUT
and B
OUT
. Resistor R
Z
plays
a special role here. In addition to ensuring that the opamps
have adequate phase margin with capacitive loads, and
thus preventing high-frequency oscillations, it serves as a
differential network. At the input amplifier, the signal from
the adjacent output amplifier is subtracted from the
summed signals on the live conductor of the cable, which is
connected to the non-inverting input of the input amplifier.
In this way, the undesired signal is eliminated in a simple
but effective manner.
In building the circuit, make sure that the
decoupling capacitors are located as
close as possible to the ICs, and arrange
the ICs and circuit tracks so that
crosstalk is minimised. Only in this way
is it possible to realise the excellent
measured results listed below. The sta-
bilised supply voltage may lie between
±
±
10
µ
Ta
47n
10
µ
Ta
47n
A
IN
B
IN
RG 59U
300m
8
8
Z
o
= 75
Ω
R11
R21
3
3
R
75
Ω
R
Z
Z
1
1
IC1.A
IC2.A
75
Ω
2
2
R12
510
Ω
R22
510
Ω
R13
R23
R14
549
R24
549
Ω
Ω
B
OUT
A
OUT
6
6
7
7
IC1.B
IC2.B
5
5
4
4
C13
C14
C13
C14
10
µ
Ta
47n
10
µ
Ta
47n
IC1 = THS4062
IC2 = THS4062
16mA
16mA
-4V5...-16V
-4V5...-16V
014016 - 11
be found at the following address:
http://www-s.ti.com/sc/psheets/slos234d/slos234d.pdf
Several interesting application notes can also be down-
loaded from the immediate ‘neighbourhood’ of the
datasheet.
(014016-1)
Technical data
Supply voltage range:
U
S
±
4.5 to
±
16
V
Current consumption
I
S
16
mA
Bandwidth (–3 dB)
GBW
180
MHz
Bandwidth (–0.1 dB) (G = +1)
BW
75
MHz
Slew rate
SR
400
V/µs
Offset voltage
U
ios
2.5
mV
16 V, and the maximum cur-
rent load is 16 mA.
The link between the two ends is formed
by an RG-59/U cable with a characteris-
tic impedance of 75
4.5 V and
±
Offset drift
15
µV/K
Distortion
THD+N
–72
dBc
Common-mode rejection
CMRR
110
dB
Phase error
0.02
degree
, which may be up
to 300 m long. If a twisted-pair cable is
used, the value of R
Z
may be reduced (
Gain error
0.02
%
Noise
e
n
14.5
nV/
√
Hz
Output Current
I
out
115
mA
Operating temperature THS4062xx
CD (SOP8)
0 to 70
°C
20
).
The data sheet for this interesting video
opamp (and for a single opamp with the
same characteristics, the THS4061), can
CDGN (SSOP8)
0 to 70
°C
ID (SOP8)
–40 to +85
°C
IDGN (SSOP8)
–40 to +85
°C
12/2001
Elektor Electronics
31
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