that1286 THAT Corporation, that1286 Datasheet - Page 5

• Manufacturer Part Number: that1286
• Description: Dual Balanced Line Receiver Ics
• Manufacturer: THAT Corporation

THAT 1280 Series
Dual Balanced Line Receiver ICs
in absolute value of any individual resistor, RF
bypassing through the addition of R-C networks at
the inputs (series resistor followed by a capacitor to
ground at each input) is not recommended.
added resistors can interact with the internal ones in
unexpected ways.
RF-bypass capacitor to work against is deemed
necessary, THAT recommends the use of a ferrite
bead or balun instead.
1280-series parts, the coupling capacitors should be
sized to present negligible impedance at any frequen-
cies of interest for common mode rejection. Regard-
less of the type of coupling capacitor chosen,
variations in the values of the two capacitors,
working against the 1280-series input impedance
(itself subject to potential imbalances in absolute
value, even when trimmed for perfect ratio match),
can unbalance common mode input signals. This can
convert common-mode to balanced signals which will
not be rejected by the CMRR of the devices. For this
reason, THAT recommends dc-coupling the inputs of
the 1280-series devices.
Input Voltage Limitations
-6 dB gain, the 1283 and 1286 devices are capable of
accepting input signals above the power supply rails.
This is because the internal opamp’s inputs connect
to the outside world only through the on-chip resis-
tors R
Figure 2. Consider the following analysis.
Differential Input Signals
signal handling will be output clipping. The outputs
of all the devices typically clip at within 2V of the
supply rails. Therefore, maximum differential input
signal levels are directly related to the gain and
supply rails and can be calculated in dBu as follows:
V
V
Gain = -3 dB, then
Common-Mode Input Signals
tially no output signal. The limitation on common-
mode handling is the point at which the inputs are
overloaded. So, we must consider the inputs of the
opamp.
input current splits to flow through both R
V
in(diff)
in(diff)
in(diff)
or
For example, If V
If it is necessary to ac-couple the inputs of the
When configured, respectively, for -3 dB and
For differential signals (v
For common-mode input signals, there is essen-
For common-mode signals (V
1
= 20 log
= 20 log(V
= 20 log[15V − (−15V) − 4V] − (−3dB) − 6.8dB
through R
= 24.5 dBu
V CC −V EE
CC
0.775
4
2
− V
2
CC
at nodes a and b as shown in
If some impedance
=15V, V
−2V
EE
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
− Gain
− 4V) − Gain − 6.8dB
IN(DIFF)
EE
IN(CM)
=-15V, and
), the common-mode
), the limitation to
1
/R
Copyright © 2007, THAT Corporation
2
and through
for the
The
Page 5 of 10
R
consider only the voltage at node a.
(R
Furthermore, the same constraints apply to v
the differential analysis.
maximum common-mode input signal for the 1280 is
(2V
the 1283, these figures are (2.4V
(2.4V
(3V
rails, the 1280 will accept up to ~26 V in either
direction. As an ac signal, this is 52 V peak-peak,
18.4 V rms, or +27.5 dBu. With the same supply
rails, the 1283 will accept up to ~31 V in either
direction. As an ac signal, this is 62 V peak-peak,
21.9 V rms, or +29 dBu. With the same supply rails,
the 1286 will accept up to ~39 V in either direction.
As an ac signal, this is 78 V peak-peak, 27.6 V rms,
or +31 dBu.
common-mode signals combine. The maximum
signal that can be accommodated will depend on the
superposition of both differential and common-mode
limitations.
Output Considerations
supplying 42 mA into a short circuit. While they will
survive a short, power dissipation will rise dramati-
cally if the output is shorted. Junction temperature
must be kept under 125 ºC to maintain the devices’
specifications.
load capacitance over the entire rated temperature
range, and even more at room temperature.
Power Supply Considerations
tive to the power supply, but they do contain wide
bandwidth opamps. Accordingly, small local bypass
capacitors should be located within a few inches of
the supply pins on these parts, as shown in Figure 4.
Selecting a Gain Variation
structures to suit different applications. The 1286 is
customarily configured for -6 dB gain, but by revers-
ing the resistor connections, it can also be configured
for +6 dB. The 1283 is most often configured for
-3 dB gain, but can also be configured for +3 dB.
The choice of input gain is determined by the input
3
/R
3
CC
CC
+ R
4
The voltage at a can be calculated as:
V
Solving for v
V
For the 1280, (R
Following the same reasoning as above, the
Therefore, for common-mode signals and ±15 V
Of course, in the real world, differential and
The 1280-series devices are typically capable of
These devices are stable with up to 300 pF of
The 1280-series parts are not particularly sensi-
The three different parts offer different gain
.
EE
- 6) V, and (3V
- 4) V, and the minimum is (2V
a
IN(CM)
Because v
= V
4
+ 4.8) V.
) /R
= V
IN(CM)
4
= 2.4. For the 1286, (R
a
IN(CM)
R
b
R
3
3
R
R
+R
is constrained to follow V
+R
4
4
For the 1286, these figures are
EE
4
,
4
3
+ 6) V.
+ R
4
) /R
Document 600114 Rev 01
4
= 2. For the 1283,
CC
3
EE
- 4.8) V, and
+ R
+ 4) V. For
4
) /R
a
, we will
a
4
as in
= 3.