THAT1200P08-U THAT Corporation, THAT1200P08-U Datasheet - Page 4

• Manufacturer Part Number: THAT1200P08-U
• Description: LINE RECEIVER, BALANCED, 1200, DIP8
• Manufacturer: THAT Corporation

Specifications of THAT1200P08-U

• Device Type: Differential
• Supply Voltage Range: ± 3V To ± 18V
• Driver Case Style: DIP
• No. Of Pins: 8
• Operating Temperature Range: 0°C To +85°C
• Operating Temperature Max: 85°C
• Operating Temperature: RoHS Compliant
• Bandwidth: 22MHz
• Base Number: 1200
• Rohs Compliant: Yes

Page 4
limitations of traditional approaches to active input
stage design. Because of the many misconceptions
about the performance of conventional input stages,
and to set the stage for discussion of InGenius, we
will begin by discussing conventional approaches.
Traditional Balanced Input Stages
professional audio products is shown in figure 3. It
amplifies
mon-mode interference based on the precision of the
match in the ratios R
1240 series), these resistor ratios are trimmed (usu-
ally with a laser) to extreme precision, resulting in
typical match of ±0.005%. So, one can assume that
R
mula as follows:
CMRR Depends on Resistor Match
source, the precisely matched resistor ratios deliver
extremely high CMRR. With perfectly matched resis-
tor ratios, for V
differential input signal), then V
On the other hand, for V
a pure common mode signal), then V
duces an infinite common mode rejection ratio. Any
difference between the ratios R
lead to less than perfect CMRR.
2
/R
The InGenius concept was invented to overcome
The typical balanced input stage used in most
In modern integrated circuits (such as the THAT
V
yielding:
V
When driven from a theoretical, true voltage
Vdiff
V
1
out
out
out
=R
=
=
4
=
/R
(
[
(
V
(
Figure 3. Basic differential amplifier
V
V
differential
3
in
. In this case, we can simplify this for-
in
in
+
+
+
)(
)(
) (
1
in+
+
1
+
+
V
R
R
=-V
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
R
R
Vin-
Vin+
1
in
2
1
2
)(
2
−
)
/R
R
R
)
in-
(
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
]
R
1
2
1
)
R
R
signals
3
in+
R
(this corresponds to a pure
1
and R
(
2
+
1
R1
R3
4
R
+
=V
1
4
R
R
1
)
2
)
+
in-
+
4
(
/R
V
(
2
V
(this corresponds to
in
but
out
/R
3
in
−
. In this circuit,
−
1
=2*(V
)
+
-
out
)
R
R
and R
R
R
1
R4
2
R2
=0. This pro-
1
rejects
2
Theory of Operation
in+
4
)*R
/R
3
Vout
2
com-
/R
will
1
.
The Impact of Driving Source Impedance
non-zero output impedance, the situation is more
complicated. Figure 4 shows the equivalent circuit of
a real-world differential application. In this case, the
source connected to the differential receiver has
source impedance of R
in the negative side. Because these two resistive ele-
ments are in series with each other, they only serve to
attenuate the signal V
ance of the differential stage. Even if they (Rs+ and
Rs-) are mismatched, this attenuation is the only con-
sequence of non-zero source impedance.
mon-mode interference. Common-mode signals ap-
pear in phase between the two input terminals. For
in-phase signals, the source impedances can have
significant impact. As shown in Figure 5, this is be-
cause each leg of the source impedance forms a volt-
age divider when it interacts with the input
impedance of its respective input of the differential
amplifier.
plifier are forced by feedback to maintain the same
voltage, the individual common-mode impedances of
each side of the differential stage are:
a load for common-mode input signals, are identical.
(This is why, in discrete applications, it is wise to
choose R
tions, these resistors are chosen to be the same
value.)
InGenius High CMRR-Balanced Input Line Receiver IC
However, in the real world, where sources have
However, the same cannot be said for com-
Because the + and - inputs of the operational am-
Z
Z
So long as R
The total common-mode input impedance is
CM +
CM
+
+
-
-
Vdiff
Figure 4. Basic differential amplifier showing
Vdiff
Rs+
Rs-
−
2
2
=
=
1
=R
R
R
mismatched source impedances
3
3
R
R
+
3
1
+
3
, and why, in all integrated applica-
R
R
4
1
=R
4
.
; and
3
, these impedances, which form
diff
Vin-
Vin+
s+
relative to the input imped-
in the positive side, and R
R1
R3
+
-
R4
R2
Vout
s-