THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

Tel: +1 (508) 478-9200; Fax: +1 (508) 478-0990; Web: www.thatcorp.com

THAT 1200, 1203, 1206

Description

The THAT 1200 series of InGenius balanced

line receivers are designed to overcome a serious
limitation of conventional balanced input stages
-- notoriously poor common mode rejection in
real world applications. While conventional input
stages may exhibit good rejection characteristics
in the lab and on paper, they perform poorly
when fed from even slightly unbalanced source
impedances -- a common situation in almost any
pro sound environment.

Developed by Bill Whitlock of Jensen Trans-

formers, the patented InGenius input stage uses a
unique bootstrap circuit to raise its common-
mode input impedance into the megohm range,
but without the noise penalty that comes from
high-valued resistors. InGenius line receivers
maintain their high CMRR over a wide range of
source impedance imbalances -- even when fed
from single-ended sources.

T H A T

C o r p o r a t i o n

InGenius

High-CMRR

Balanced Input Line Receiver

FEATURES

High common-mode rejection
(typical 90 dB at 60 Hz) maintained
under real-world conditions

Excellent solution for hum and
groundloop suppression

Transformer-like noise rejection in
an 8-pin IC, at fraction of
transformer cost and size

APPLICATIONS

Balanced input stages

Summing amplifiers

Transformer front-end
replacements

ADC front-ends

IN-

IN+

REF

CM OUT

Vcc

Vee

Vout

CM IN

OA1

OA2

OA3

OA4

Figure 1. THAT1200-series equivalent circuit diagram

Pin Name

DIP Pin

SO Pin

Ref

In-

In+

Vee

CM In

Vout

Vcc

CM Out

Table 1. 1200-series pin assignments

Gain

Plastic DIP

Plastic SO

0 dB

1200P

1200S

-3 dB

1203P

1203S

-6 dB

1206P

1206S

Table 2. Ordering information

Protected under U.S. Patent No. 5,568,561 and other patents pending.

InGeniusâ is a trademark of THAT Corporation.

600033 Rev 0A

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

Tel: +1 (508) 478-9200; Fax: +1 (508) 478-0990; Web: www.thatcorp.com

Page 2

InGenius Balanced Line Receiver

Preliminary Information

Absolute Maximum Ratings (T

= 25°C)

Positive Supply Voltage (V

)

+18 V

Power Dissipation (P

) (T

= 75°C)

TBD mW

Negative Supply Voltage (V

)

-18 V

Operating Temperature Range (T

)

0 to +70°C

Positive Input Voltage (V

IN+

)

+18 V

Storage Temperature Range (T

)

-40 to +125°C

Negative Input Voltage (V

IN-

)

-18 V

Junction Temperature (T

)

150°C

Output Short-Circuit Duration (t

)

Continuous

Lead Temperature (Soldering 60 seconds)

TBD °C

Electrical Characteristics

Parameter

Symbol

Conditions

Min

Typ

Max

Units

Supply Current

No signal

4.7

8.0

Input Bias Current

No signal; Either input

700

1,400

connected to GND

Input Offset Current

B-OFF

No signal

±140

Input Offset Voltage

OFF

No signal

Input Voltage Range

IN-CM

Common mode

±12.5

±13.0

IN-DIFF

Differential (equal and opposite swing)

THAT 1200

21.0

21.5

dBu

THAT 1203

24.0

24.5

dBu

THAT 1206

24.0

24.5

dBu

Input Impedance

IN-DIFF

Differential

48.0

IN-CM

Common mode

with bootstrap

60 Hz

10.0

20 kHz

3.2

no bootstrap

60 Hz

36.0

20 kHz

36.0

Recommended Operating Conditions

Parameter

Symbol

Conditions

Min

Typ

Max

Units

Positive Supply Voltage

+18

Negative Supply Voltage

-3

-18

SPECIFICATIONS

1. All specifications are subject to change without notice.

2. Unless otherwise noted, T

=25°C, V

= +15V, V

= -15V

3. 0 dBu = 0.775Vrms.

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

Tel: +1 (508) 478-9200; Fax: +1 (508) 478-0990; Web: www.thatcorp.com

600033 Rev 0A

Page 3

Preliminary Information

Electrical Characteristics (Cont'd)

Parameter

Symbol

Conditions

Min

Typ

Max

Units

Common Mode Rejection

CMR

Matched source impedances; V

= ±10V

60 Hz

20 kHz

Common Mode Rejection

CMR

600

W unmatched source impedances

; V

= ±10V

60 Hz

20 kHz

Power Supply Rejection

PSR

At 60 Hz, with V

= -V

THAT1200

THAT1203

THAT1206

Power Supply Rejection

PSR

At CM output, at 60 Hz

Total Harmonic Distortion

THD

IN-DIFF

= 10 dBV; BW = 20 kHz; f = 1 kHz

RL =2 k

0.0005

Output Noise

n(OUT)

BW = 20 kHz

THAT1200

-106

dBu

THAT1203

-105

dBu

THAT1206

-107

dBu

Output Noise

nCM(OUT)

At CM output

-106

dBu

Slew Rate

= 10 k

W; C

= 300 pF

V/µs

Slew Rate

With CM input signal

12.5*

V/µs

Lcm

= 10 k

W; C

Lcm

= 50 pF

Small Signal Bandwidth

-3dB

= 10 k

W; C

= 10 pF

THAT1200

MHz

THAT1203

MHz

THAT1206

MHz

= 2 k

W; C

= 300 pF

THAT1200

MHz

THAT1203

MHz

THAT1206

MHz

Small Signal Bandwidth

CM-3dB

At CM output; R

Lcm

= 10 k

Lcm

= 10 pF

MHz

Lcm

= 50 pF

MHz

Output Gain Error

ER(OUT)

f = 1 kHz; R

= 2 k

±0.05

Output Voltage Swing

At max differential input

THAT1200

21.5

dBu

THAT1203

21.5

dBu

THAT1206

18.5

dBu

4. See test circuit in Figure 2.

5. Defined with respect to the differential gain.

6. Defined with respect to the common mode gain between any input and common mode output.

* Guaranteed by design

Applications

RFI Protection

Figure 3 shows the THAT 1200 configured with

robust RFI input protection.

In applications where

RFI rejection is of less concern, the circuit shown Fig-
ure 4 provides a less aggressive approach.

Bootstrap coupling capacitor

Referring to Figure 3, electrolytic capacitor Cb

provides the feedback path for the boostrap circuit.
The capacitor value is chosen to be high enough to
present a sufficiently small impedance to signals at

the low end of the audio spectrum. Its voltage rating
is dependent on the topology of the surrounding cir-
cuitry, as described in the following paragraphs.

AC signals presented to the input stage cause the

two ends of capacitor Cb to swing in tandem so that
virtually no voltage appears across the capacitor.
Consequently, capacitors with small DC working volt-
ages may be used when the previous stage is AC cou-
pled to the input of the THAT 1200.

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

Tel: +1 (508) 478-9200; Fax: +1 (508) 478-0990; Web: www.thatcorp.com

Page 4

InGenius Balanced Line Receiver

Preliminary Information

Electrical Characteristics (Cont'd)

Parameter

Symbol

Conditions

Min

Typ

Max

Units

Output Short Circuit Current

= R

Lcm

= 0

±25

CMSC

At CM output

±10

Minimum Resistive Load

Lmin

LCMmin

At CM output

Maximum Capacitive Load

Lmax

300

LCMmax

At CM output

In-

In+

CMin

Out

THAT120x

100u

56p

C2
300p

100n

200k

R2
200k

600R

R4
2k

100R

Vcc

Vee

In-

In+

Ext. DC Source

CM Out

Main Out

Gnd

CMout

Vcc

Ref

Vee

Figure 2. THAT1200-series test circuit

If, however, there is the possibility of a DC voltage

appearing across the inputs of the line receiver, a
portion of that voltage will appear directly across the
terminals of capacitor Cb. In that case, choose the

capacitor's voltage rating so that it is capable of han-
dling the expected level of DC voltage. If the polarity
of the DC voltage is unknown, or may swing to either
polarity, the use of a non-polarized electolytic is
highly recommended.

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

Tel: +1 (508) 478-9200; Fax: +1 (508) 478-0990; Web: www.thatcorp.com

600033 Rev 0A

Page 5

Preliminary Information

IN-

IN+

OUT

CM
IN

OUT

REF

VCC

VEE

220uF

5 4

3 1

J1
XLR-F

Vcc

Vee

OUT

100pF NPO

Vcc

Vee

12V

Figure 4. THAT1200P showing simplified RFI protection scheme

IN-

IN+

OUT

REF

VCC

VEE

4k7

220uF

470pF

100pF

5 4 3 1

J1
XLR-F

Vcc

Vee

OUT

100R

(see text)

optional RFI protection

Vcc

Vee

12V

Figure 3. THAT1200P typical application circuit

Dual Layout Option

The THAT 1246 is a conventional balanced

line-receiver that is pin-for-pin compatible with the
Analog Devices SSM2143 and Burr-Brown INA137.
Though the THAT 1200 series is not pin-compatible
with the THAT 1246, the PCB layouts shown in Fig-
ures 5 and 6 provide manufacturers with the option
to stuff a PCB with any of these input stages. Note
that these figures are not to scale. The interconnects
should be as short as practicable constrained only by
component size and relevant manufacturing consid-
erations.

When a THAT 1200 series IC is installed, capaci-

tor Cb is connected between CM In and CM Out.
When the THAT 1246 (or SSM2143 or INA137) is
used, capacitor Cb is removed, and a jumper con-
nects the Vout and Sense pins.

Input Protection

Figure 7 shows the internal overvoltage protection

circuitry at the IN+, IN-, and CM IN pins. The values
of R and R' vary with actual part number as shown in
Table 3.

While the internal protection circuitry shown is

adequate to keep the combination of signal and com-
mon mode voltages from driving the internal inputs
beyond the power supply rails, the circuitry does not
provide adequate protection against most ESD inci-
dents. Since these ICs will very often connect directly
to the outside world, it is mandatory that additional,
external protection from ESD be provided. Any un-
protected InGenius input will fail when subjected to
ESD if this protection circuitry is omitted.

Addi-

tionally, proper ESD handling precautions must be
observed until the IC is properly affixed to the PCB.

Diodes D1-D6 in figures 3 and 4 show our recom-

mended approach to protecting the 1200 series from
ESD damage.

This arrangement of 1N4148s and

12V Zener diodes permits the maximum allowable
input signal to reach the IC's input pins, but directs
high-energy ESD impulses to the rails. So long as the
supply rails are adequately decoupled, most ESD
events will be diminished to harmless levels.

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

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Page 6

InGenius Balanced Line Receiver

Preliminary Information

Vcc

Vee

IN+

IN-

CM IN

Vee

Figure 7. Internal input protection circuitry (see text)

Part No.

THAT 1200

500

23.5k

THAT 1203

17k

THAT 1206

17k

Table 3. Input resistance values

Vcc

Gnd

In-

In+

Vee

CM out or N/C

Vcc

Vout

CM in or Sense

Connect
for
THAT1246

Ref

In-

In+

Vee

THAT1206

or THAT1246

Figure 5. Dual PCB layout for THAT 1206 and THAT 1246

DIP version

Vcc

Gnd

In-

In+

Vee

CM Out

Vcc
Vout

CM in

Connect
for
THAT1246

Ref
In-

In+

Vee

THAT1246

THAT1206

N/C

Vout

Sense

Vee

Vcc

Figure 6. Dual PCB layout for THAT 1206 and THAT 1246

Surface mount versions

Theory of Operation

Conventional high-CMRR balanced input stages

cancel common-mode interference using a differential
amplifier with matched (trimmed) resistance ele-
ments (Figure 8). When driven from a true voltage
source, these conventional stages offer extremely high
CMRR (>80dB).

However, when driven from real-

world sources, the CMRR of these stages degrades
rapidly for even small source impedance imbalances.

The reason why this occurs is easily shown. Fig-

ure 9 shows that a voltage divider is formed between
the impedance of the external signal source and the
input impedance of the differential amplifier.

For

perfectly balanced source impedances (Rs1 = Rs2),
and

perfectly

balanced

input

impedances

(Ri1 = Ri2), the voltage dividers formed at each node

(

and

) will be equal to each other,

so the conventional input stage will maintain high
CMRR.

However, if the source impedances are not pre-

cisely equal, the voltage divider action will result in
unequal signals at the plus and minus inputs of the
input stage. In this case, no amount of CMRR is suf-
ficient to reject the differential voltage that is gener-
ated by the impedance mismatch.

To illustrate, consider Figure 10.

A common

mode input signal is shown as Vcm. It couples to the
positive and negative input of the balanced line re-
ceiver via Rs1 and Rs2, repectively.

Typically, con-

ventional balanced line receivers have common-mode

input impedances of approximately 10 k

W. In such

cases, a source impedance imbalance of only 10

can degrade CMRR to about 65 dB.

A 10

W mis-

match may be easily caused by tolerances in coupling
capacitors or output resistors, and variations in con-
tact and wire resistance. The situation becomes even
worse when a conventional balanced line receiver is
driven from an unbalanced source.

The best solution to this problem is to increase

the line receiver's common-mode input impedance
enough to minimize the imbalanced voltage divider
effect, preferably on the order of several megohms.
However, with a conventional differential amplifier,
this requires the use of high resistances in the cir-
cuit. High resistance carries with it a high noise pen-
alty,

making

this

straightforward

approach

impractical for quality audio devices.

An alternative approach is to use the classic in-

strumentation amplifier configuration shown in Fig-
ure 11.

In this circuit, the common-mode input

impedance is the parallel combination of Ri1 and
Ri2.

Unfortunately for this approach, to achieve

multi-megohm input impedances, the input devices
used in the input amplifiers must have extremely low

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

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600033 Rev 0A

Page 7

Preliminary Information

Rs1

Rs2

Rs1 Rs2

Vout

+Vin

-Vin

Ri1

Ri2

Vcm

Figure 10. Basic differential amplifier driven

by common-mode input signal

Rs1

Rs2

Rs1

¹R

Vout

+Vin

-Vin

Ri1

Ri2

Figure 9. Basic differential amplifier showing

mismatched source impedances

Vout

+Vin

-Vin

Ri1

Ri2

Figure 8. Basic differential amplifier

bias currents since their input bias flows through Ri1
and Ri2. Because of the difficulty of maintaining low
noise with low input bias currents, FET op amps
may be employed, but they impose their own limita-
tions, as described further on.

The THAT 1200 series of balanced line receivers

overcomes this problem by way of an AC bootstrap
technique, shown in simplified form in Figure 12. By
driving the lower end of R2 to nearly the same AC
voltage as the upper end, AC current flow through R2
is greatly reduced, effectively increasing its value. At
DC, of course, the input impedance Z is simply R1 +
R2.

If gain G is unity, for frequencies within the

passband of the high-pass filter formed by Cb and
R1, the effective value of the input impedance is in-
creased to infinity at sufficiently high frequencies.

Input impedance Z, at frequency f, is described

the following equation:

+ -

(

)

(

)

(

) (

)

where

R C

(

)

For example, if R1 and R2 are 10 k

W each, Z

20 k

W. This resistance provides a DC path for am-

plifier bias current as well as leakage current that
might flow from a signal source. At higher frequen-
cies, the bootstrap greatly increases the input imped-
ance,

limited

ultimately

how

gain

approaches unity. With the THAT 1200 input stages,
common-mode input impedances of several meg-
ohms across much of the audio spectrum can be ex-
pected.

Figure 1 shows a complete equivalent circuit for

the THAT 1200-series ICs.

OA1 and OA2 are

high-impedance buffers feeding differential amplifier
OA3 in an instrumentation amplifier configuration.
The common mode signal is extracted at the junction
of Rc and Rd, buffered by OA4, and fed back to both
inputs via capacitor Cb and resistors Ra and Rb.
The junction of Ra, Rb and R5 is driven to the same
potential as the common-mode input voltage. Hence
no common-mode current flows in resistors Ra and
Rb. Since, ideally, no current flows, the input imped-
ance to common mode signals is infinite.

The effectiveness of this topology is limited by the

unity gain precision of OA4 and the input imped-
ances of OA1 and OA2, all of which are optimized in
THAT's integrated circuit process.

Note that OA1

and OA2 isolate OA3 from external source imped-
ances. Therefore, the performance of the differential
amplifier OA3 and its associated components are not
affected by imbalances in the source impedances.

Alternatives

In the following section we will compare other so-

lutions for minimizing CMRR degradation in the
presence of source impedance mismatch, and con-
trast them with THAT's InGenius topology.

Precision 4-resistor op amp stage

This stage (Figure 8) was discussed earlier.

summarize, this solution offers high common-mode
rejection only when the source impedances are per-
fectly balanced, or a tiny fraction of the common-
mode input impedance.

Because differential- and

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

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Page 8

InGenius Balanced Line Receiver

Preliminary Information

G = 1

Figure 12. InGenius bootstrap topology

Out

+ In

- In

OA1

OA2

OA3

Ri1

Ri2

Figure 11. Instrumentation amplifier

common-mode input impedances are inextricably
linked, and of similar magnitude, it is not possible to
increase common-mode input impedance without
compromising noise performance.

3-op amp instrumentation amplifier

This topology, shown in Figure 11, was also dis-

cussed earlier.

It relies on input buffers OA1 and

OA2 to raise the common-mode and differential-
mode input impedances.

The following diff amp,

OA3 (which can be of the precision 4-resistor op amp
type), is then used to reject the common-mode signal
while extracting the differential signal.

This approach will require reasonably low values

for Ri1 and Ri2 (< 100 k

W or so) unless the OA1 and

OA2 use FETs at their inputs. This would limit the
common-mode input impedance to a few hundred
kilohms.

If FET-input devices are used for OA1 and OA2,

Ri1 and Ri2 can be made quite large -- on the order
of 10 megohms. Unlike the resistors in the conven-
tional diff amp stage, these resistors will be shunted
by the driving source impedance, and so contribute
negligible noise.

At first glance, this might seem to be an excellent

solution.

However, there are disadvantages to this

approach.

First, the designer must select a FET-

input op amp that is low-noise and that exhibits no
phase inversion (sign reversal) with large differential-
and common-mode signal swings.

This, of course,

results in a cost penalty that is somewhat exacer-
bated by the price premium for high-value resistors.

Second, this design requires at least two IC pack-

ages -- a dual FET op amp and the precision input
stage.

Third, while the large-value input resistances are

shunted when there is a source connected to the
input, there is no guarantee that long cables will al-
ways be properly terminated. With an unterminated
cable plugged into the associated XLR jack, Ri1 and
Ri2 are no longer shunted and become not only large
noise sources themselves, but will do little to reduce
pickup on the cable.

The THAT 1200-series input stages avoid these

problems altogether.

They exhibit high common-

mode input impedance as a result of their boot-
strapped topology, while maintaining reasonable dif-
ferential input resistances that can be left unshunted
with no fear of stray pickup or excessive noise contri-
bution.

Transformers

When true electrical isolation is required, a trans-

former may be the only solution. Transformers suit-
able for pro audio, however, tend to be costly and
take up valuable board real estate. In addition, some
transformers can color the sound in ways that elec-
tronic solutions do not.

Fortunately, it is usually not the case that galvanic

isolation is required, and in most cases it is the
common-mode signal rejection properties of a trans-
former that is sought after.

By providing the high

common-mode input impedance of a transformer
with the size and cost of an 8-pin integrated circuit,
the THAT 1200-series provides designers with an al-
ternative that provides excellent interference rejection
in real-world applications.

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

Tel: +1 (508) 478-9200; Fax: +1 (508) 478-0990; Web: www.thatcorp.com

600033 Rev 0A

Page 9

Preliminary Information

Package Information

The THAT 1200 series is available in both 8-pin

mini-DIP and 16-pin SOIC packages.

The package

dimensions are shown in Figures 13 and 14, while
pinouts are given in Table 1.

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

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Page 10

InGenius Balanced Line Receiver

Preliminary Information

ITEM

A
B
C
D
E
F
G
H
J

MILLIMETERS
10.11/10.31
7.40/7.60
10.11/10.51
0.36/0.46
1.27
2.44/2.64
0.23/0.32
0.51/1.01
0.10/0.30

INCHES
0.398/O.406
0.291/0.299
0.398/0.414
0.014/0.018
0.050
0.096/0.104
0.009/0.013
0.020/0.040
0.004/0.012

Figure 14. -S (SO) version package outline drawing

ITEM

A
B
C
D
E
F
G
H
J
K

MILLIMETERS
9.52 0.10
6.35 0.10
7.49/8.13
0.46
2.54
3.68/4.32
0.25
3.18 0.10
8.13/9.40
3.30 0.10

±
±

INCHES
0.375
0.250 0.004
0.295/0.320
0.018
0.100
0.145/0.170
0.010
0.125 0.004
0.320/0.370
0.130 0.004

±0.004
±

Figure 13. -P (DIP) version package outline drawing

Information furnished by THAT Corporation is believed to be accurate and reliable. However no responsibil-

ity is assumed by THAT Corporation for its use nor for any infringements of patents or other rights of third par-
ties which may result from its use.

LIFE SUPPORT POLICY

THAT Corporation products are not designed for use in life support equipment where malfunction of such

products can reasonably be expected to result in personal injury or death. The buyer uses or sells such prod-
ucts for life suport application at the buyer's own risk and agrees to hold harmless THAT Corporation from all
damages, claims, suits or expense resulting from such use.

CAUTION: THIS IS AN ESD (ELECTROSTATIC DISCHARGE) SENSITIVE DEVICE.

It can be damaged by the currents generated by electrostatic discharge. Static charge and therefore danger-

ous voltages can accumulate and discharge without detection causing a loss of function or performance to occur.

The transistors in this device are unprotected in order to maximize performance and flexibility. They are

more sensitive to ESD damage than many other ICs which include protection devices at their inputs.

Use ESD preventative measures when storing and handling this device. Unused devices should be stored in

conductive packaging. Packaging should be discharged before the devices are removed. ESD damage can occur
to these devices even after they are installed in a board-level assembly. Circuits should include specific and ap-
propriate ESD protection.

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: THAT1200S

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: THAT1200S