SGM621
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
GENERAL DESCRIPTION
FEATURES
The SGM621 is a high accuracy, high voltage
● Single External Resistor Gain Set
instrumentation amplifier, which is designed to set any
(Set Gain from 1 to 10000)
gain from 1 to 10000 with one external resistor. The
● Input Offset Voltage: 150μV (MAX)
device works well in battery-powered applications due to
● Input Bias Current: 15nA (TYP)
the low power consumption of 1.3mA typical quiescent
● Common Mode Rejection Ratio: 105dB (TYP) (G = 10)
current. The SGM621 provides SOIC-8 and MSOP-8
● Input Voltage Noise: 6nV/√Hz at 1kHz
packages which are much smaller than discrete
● 0.1Hz to 10Hz Voltage Noise: 0.4μVP-P
classical-three-OPAs circuits.
● Bandwidth: 140kHz (G = 100)
The SGM621 provides 120ppm (MAX) non-linearity
and 150μV (MAX) low input offset voltage. The device
also features low noise, low bias current and low power.
The combination of these characteristics makes it a
good choice for applications requiring excellent DC
performance.
The SGM621 offers 6nV/√Hz low input voltage noise,
300fA/√Hz input current noise at 1kHz, and 0.4μVP-P in
the 0.1Hz to 10Hz band. It is suitable for pre-amplifier
applications. The 10μs settling time to 0.01% makes
SGM621 appropriate for multiplexed applications.
● Settling Time to 0.01%: 10μs (G = 100)
● Rail-to-Rail Output
● Support Single or Dual Power Supplies:
4.6V to 36V or ±2.3V to ±18V
● Low Power Supply Current: 1.3mA (TYP)
● -40℃ to +125℃ Operating Temperature Range
● Available in Green SOIC-8 and MSOP-8 Packages
APPLICATIONS
Precision Current Measurement
Pressure Measurement
The SGM621 is available in Green SOIC-8 and
MSOP-8 packages. It is specified over the extended
-40℃ to +125℃ temperature range.
SG Micro Corp
www.sg-micro.com
JUNE 2022 – REV. A. 2
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
PACKAGE/ORDERING INFORMATION
MODEL
PACKAGE
DESCRIPTION
SPECIFIED
TEMPERATURE
RANGE
ORDERING
NUMBER
SOIC-8
-40℃ to +125℃
SGM621XS8G/TR
MSOP-8
-40℃ to +125℃
SGM621XMS8G/TR
SGM621
PACKAGE
MARKING
SGM
621XS8
XXXXX
SGM621
XMS8
XXXXX
PACKING
OPTION
Tape and Reel, 4000
Tape and Reel, 4000
MARKING INFORMATION
XXXXX = Date Code, Trace Code and Vendor Code.
XXXXX
Vendor Code
Trace Code
Date Code - Year
Green (RoHS & HSF): SG Micro Corp defines "Green" to mean Pb-Free (RoHS compatible) and free of halogen substances. If
you have additional comments or questions, please contact your SGMICRO representative directly.
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, +VS to -VS............................................... 40V
Input Common Mode Voltage .......................................... ±VS
Junction Temperature .................................................+150℃
Storage Temperature Range........................ -65℃ to +150℃
Lead Temperature (Soldering, 10s) ............................+260℃
ESD Susceptibility
HBM ............................................................................. 7000V
CDM ............................................................................ 1000V
RECOMMENDED OPERATING CONDITIONS
Operating Temperature Range ..................... -40℃ to +125℃
OVERSTRESS CAUTION
ESD SENSITIVITY CAUTION
This integrated circuit can be damaged if ESD protections are
not considered carefully. SGMICRO recommends that all
integrated circuits be handled with appropriate precautions.
Failure to observe proper handling and installation procedures
can cause damage. ESD damage can range from subtle
performance degradation to complete device failure. Precision
integrated circuits may be more susceptible to damage
because even small parametric changes could cause the
device not to meet the published specifications.
DISCLAIMER
SG Micro Corp reserves the right to make any change in
circuit design, or specifications without prior notice.
Stresses beyond those listed in Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to
absolute maximum rating conditions for extended periods
may affect reliability. Functional operation of the device at any
conditions beyond those indicated in the Recommended
Operating Conditions section is not implied.
SG Micro Corp
www.sg-micro.com
JUNE 2022
2
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
PIN CONFIGURATIONS
(TOP VIEW)
IN-
1
RG
2
RG
3
IN+
4
8
+VS
_
7
OUT
+
6
REF
5
-VS
SOIC-8/MSOP-8
PIN DESCRIPTION
PIN
NAME
1
IN-
Inverting Input Pin.
2, 3
RG
Gain Setting Pin. The gain can be set by placing the resistor across RG.
G = 1 + (49.4kΩ/RG).
4
IN+
Non-Inverting Input Pin.
5
-VS
Negative Power Supply Pin.
6
REF
Voltage Reference Pin. A voltage source with low impedance can be placed to supply this
terminal in order to shift the output level.
7
OUT
Output Pin.
8
+VS
Positive Power Supply Pin.
SG Micro Corp
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FUNCTION
JUNE 2022
3
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
ELECTRICAL CHARACTERISTICS
(VS = ±15V, RL = 2kΩ, Full = -40℃ to +125℃, typical values are at TA = +25℃, unless otherwise noted.)
PARAMETER
Gain (G = 1 + (49.4kΩ/RG))
Gain Range
SYMBOL
CONDITIONS
TEMP
TYP
1
G=1
G = 10
Gain Error (1)
MIN
GE
VOUT = -10V to +10V
G = 100
G = 1000
G=1
G>1
Gain Temperature Coefficient
G=1
G = 10
Non-Linearity
VOUT = -10V to +10V
G = 100
G = 1000
UNITS
10000
0.01
+25℃
MAX
Full
0.1
0.15
0.15
+25℃
Full
0.3
0.6
0.15
+25℃
Full
0.3
%
0.6
+25℃
0.15
Full
Full
Full
1
20
+25℃
10
0.6
0.8
Full
ppm/℃
70
100
10
+25℃
Full
70
100
10
+25℃
Full
70
ppm
100
20
+25℃
Full
120
170
Voltage Offset (Total RTI Error = VOSI + VOSO/G)
Input Offset Voltage
Input Offset Voltage Drift
Output Offset Voltage
Output Offset Voltage Drift
VOSI
Full
∆VOSI/∆T
VOSO
VS = ±5V to ±15V
∆VOSO/∆T
PSRR
Full
0.2
+25℃
400
VS = ±2.3V to ±18V
G = 100
G = 1000
1200
1.5
+25℃
105
Full
102
+25℃
125
Full
122
+25℃
128
Full
125
+25℃
128
Full
125
µV
µV/℃
1600
Full
G = 10
150
200
Full
G=1
Offset Referred to the Input
vs. Supply
50
+25℃
VS = ±5V to ±15V
µV
µV/℃
110
130
dB
140
140
Input Current
Input Bias Current
Average Temperature Coefficient
of Input Bias Current
Input Offset Current
Average Temperature Coefficient
of Input Offset Current
IB
∆IB/∆T
IOS
∆IOS/∆T
+25℃
15
Full
35
Full
0.15
+25℃
5
Full
Full
25
nA/℃
20
25
0.05
nA
nA
nA/℃
NOTE: 1. Effects of external resistor RG is not included.
SG Micro Corp
www.sg-micro.com
JUNE 2022
4
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
ELECTRICAL CHARACTERISTICS (continued)
(VS = ±15V, RL = 2kΩ, Full = -40℃ to +125℃, typical values are at TA = +25℃, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
TEMP
MIN
TYP
MAX
UNITS
Input
Input
Impedance
Differential
ZDIFF
+25℃
10 || 4
Common Mode
ZCM
+25℃
10 || 4
VS = ±2.3V to ±5V
Input Voltage Range
VS = ±5V to ±18V
G=1
Common Mode Rejection Ratio
with 1kΩ Source Imbalance
G = 10
CMRR
VCM = -10V to +10V
G = 100
G = 1000
GΩ || pF
+25℃
(-VS) + 1.9
(+VS) - 1.2
Full
(-VS) + 2.1
(+VS) - 1.3
+25℃
(-VS) + 1.9
(+VS) - 1.4
Full
(-VS) + 2.1
+25℃
70
Full
67
+25℃
90
Full
87
+25℃
103
Full
100
+25℃
103
Full
100
V
(+VS) - 1.4
85
105
dB
120
120
Reference Input
Reference Input Resistance
Reference Input Current
RREF
IREF
VIN+ = VIN- = 0V, VREF = 0V
VOH
RL = 2kΩ, VS = ±18V
+25℃
18
+25℃
30
Full
kΩ
40
50
µA
Output Characteristics
+25℃
Output Voltage Swing
VOL
Short-Circuit Current
310
400
150
220
Full
600
+25℃
RL = 2kΩ, VS = ±18V
Full
ISC
VS = ±2.3V to ±18V, RL = 50Ω to VS/2
IQ
VS = ±2.3V to ±18V, IOUT = 0A
mV
300
+25℃
19
Full
14
24
mA
Power Supply
Quiescent Current
+25℃
1.3
Full
1.7
2.2
mA
Dynamic Response
Small-Signal -3dB Bandwidth
BW
Slew Rate
SR
VOUT = 1VP-P Step
tS
VOUT = 10VP-P Step
Input Voltage Noise Density
eni
f = 1kHz
Output Voltage Noise Density
eno
f = 1kHz
Settling Time to 0.01%
G=1
+25℃
3900
G = 10
+25℃
1000
G = 100
+25℃
140
G = 1000
+25℃
17
G=1
+25℃
1.2
G = 1 to 100
+25℃
10
G = 1000
+25℃
51
+25℃
6
nV/√Hz
nV/√Hz
kHz
V/µs
µs
Noise
0.1Hz to 10Hz Voltage Noise, RTI
Input Current Noise Density, RTI
0.1Hz to 10Hz Current Noise, RTI
SG Micro Corp
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+25℃
80
G=1
+25℃
6
G = 10
+25℃
1
G = 100
+25℃
0.4
G = 1000
+25℃
0.4
f = 1kHz
+25℃
300
fA/√Hz
f = 0.1Hz to 10Hz
+25℃
15
pAP-P
f = 0.1Hz to 10Hz
in
µVP-P
JUNE 2022
5
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
TYPICAL PERFORMANCE CHARACTERISTICS
At TA = +25℃, VS = ±15V, unless otherwise noted.
PSRR vs. Frequency
PSRR vs. Frequency
150
—G=1
— G = 10
— G = 100
— G = 1000
120
60
30
—G=1
— G = 10
— G = 100
— G = 1000
150
-PSRR (dB)
90
+PSRR (dB)
180
0
120
90
60
30
-30
0.1
1
10
100
0
1000
0.1
1
Frequency (kHz)
CMRR (dB)
80
RL = 2kΩ
—G=1
— G = 10
— G = 100
— G = 1000
60
Gain (dB)
120
40
0
40
20
0
0.01
0.1
1
10
100
-20
1000
0.1
1
10
Frequency (kHz)
10
1
10
100
1000
Frequency (Hz)
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1000
10000
10000
100000
Input Common Mode Voltage vs. Output Voltage
20
Input Common Mode Voltage (V)
—G=1
— G = 10
— G = 100
— G = 1000
100
100
Frequency (kHz)
Input Voltage Noise Density vs. Frequency
1000
Input Voltage Noise Density (nV/√Hz)
1000
Gain vs. Frequency
80
—G=1
— G = 10
— G = 100
— G = 1000
160
100
Frequency (kHz)
CMRR vs. Frequency
200
10
15
VS = ±15V
10
5
0
-5
VS = ±5V
-10
-15
-20
-20
-15
-10
-5
0
5
10
15
20
Output Voltage (V)
JUNE 2022
6
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
At TA = +25℃, VS = ±15V, unless otherwise noted.
0.1Hz to 10Hz Input Voltage Noise
0.1Hz to 10Hz Input Voltage Noise
G = 10
Noise (2μV/div)
Noise (300nV/div)
G=1
Time (3s/div)
Time (3s/div)
0.1Hz to 10Hz Input Voltage Noise
0.1Hz to 10Hz Input Voltage Noise
Noise (100nV/div)
G = 1000
Noise (100nV/div)
G = 100
Time (3s/div)
Time (3s/div)
10
5
5
0
10
Input
Output
0
-5
-5
-10
-15
Time (10μs/div)
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Output Voltage (V)
Output Voltage (V)
10
15
Input Voltage (V)
G = 1, RL = 2kΩ
Settling Time
15
1.5
G = 10, RL = 2kΩ
1.0
5
0
0.5
Input
Output
0.0
-5
-0.5
-10
-10
-1.0
-15
-15
-1.5
Input Voltage (V)
Settling Time
15
Time (10μs/div)
JUNE 2022
7
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
At TA = +25℃, VS = ±15V, unless otherwise noted.
Settling Time
10
Input
Output
0.00
-5
-0.05
-10
-15
5
G = 1000, RL = 2kΩ
10
5
Input
0
0
Output
-5
-5
-0.10
-10
-10
-0.15
-15
-15
Time (10μs/div)
Time (10μs/div)
Large-Signal Step Response
Large-Signal Step Response
G = 10, RL = 2kΩ, f = 10kHz
Output Voltage (1V/div)
G = 1, RL = 2kΩ, f = 10kHz
Output Voltage (1V/div)
15
Input Voltage (mV)
0
0.10
0.05
5
Time (10μs/div)
Time (10μs/div)
Large-Signal Step Response
Large-Signal Step Response
G = 1000, RL = 2kΩ, f = 1kHz
Output Voltage (1V/div)
G = 100, RL = 2kΩ, f = 5kHz
Output Voltage (1V/div)
Output Voltage (V)
10
15
Output Voltage (V)
G = 100, RL = 2kΩ
Settling Time
0.15
Input Voltage (V)
15
Time (20μs/div)
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Time (100μs/div)
JUNE 2022
8
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
At TA = +25℃, VS = ±15V, unless otherwise noted.
Small-Signal Step Response
Small-Signal Step Response
G = 10, RL = 2kΩ, f = 50kHz
Output Voltage (20mV/div)
Output Voltage (20mV/div)
G = 1, RL = 2kΩ, f = 50kHz
Time (2μs/div)
Time (2μs/div)
Small-Signal Step Response
Input Offset Voltage Production Distribution
20
16
12
8
Time (10μs/div)
Input Offset Voltage (μV)
Output Offset Voltage Production Distribution
10
5
0
Output Offset Voltage (μV)
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Input Bias Current Production Distribution
35
Percentage of Amplifiers (%)
15
-550
-500
-450
-400
-350
-300
-250
-200
-150
-100
-50
0
50
100
150
200
250
300
350
400
Percentage of Amplifiers (%)
20
7730 Samples
1 Production Lot
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
110
120
130
4
0
25
7730 Samples
1 Production Lot
28
7750 Samples
1 Production Lot
21
14
7
0
-0.2
0.6
1.4
2.2
3.0
3.8
4.6
5.4
6.2
7.0
7.8
8.6
9.4
10.2
11.0
11.8
12.6
13.4
Output Voltage (20mV/div)
Percentage of Amplifiers (%)
G = 100, RL = 2kΩ, f = 10kHz
Input Bias Current (nA)
JUNE 2022
9
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
OPERATION THEORY
The SGM621 is modified with the classic three-op-amp and it is a holistic instrumentation amplifier.
IN+
+VS
R4
400Ω
Q2
20μA
_
A2
VB
RG
+
_
20μA
18kΩ
REF
R2
+
+VS
18kΩ
C2
-VS
+
_
A3
OUT
R1
A1
C1
18kΩ
18kΩ
Q1
R3
400Ω
+VS
IN-
Figure 1. Simplified Schematic
The high precision input is provided by the two input
transistor Q1 and Q2 (Figure 1) and this results in 10 ×
lower bias current of the input pins. The constant
collector current of Q1 and Q2 is maintained by the two
loops Q1-A1-R1 and Q2-A2-R2, so the input voltage is
impressed across the gain setting resistor RG of the
amplifier. The differential gain from A1/A2 outputs can
be expressed by G = 1+ (R1+R2)/RG. The unity-gain
subtractor (A3) can reject the common mode signal so
that SGM621 produces a single-ended output with REF
pin biased.
The gain-bandwidth product which is determined by
the two capacitors C1, C2 and the transconductance of
the pre-amplifier can increase with programmed gain,
so that the frequency response is enhanced.
The transconductance of the pre-amplifier is determined
by the resistance of RG. The transconductance will
increase gradually to that of the input transistors if the
resistance of RG is reduced for larger gains. The
important benefits are shown below:
The equation of gain is shown as below:
Boosting the open-loop gain can also increase the
programmed gain, so that the related error of gain is
reduced.
SG Micro Corp
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Reducing the input voltage noise to 6nV/√Hz, and it is
determined by the base resistance and the collector
current of the input.
The integrated resistors (R1 and R2) inside the SGM621
are set to 24.7kΩ, so that the gain can be programmed
with the external resistor RG.
49.4kΩ
+1
RG
49.4kΩ
RG =
G-1
G=
JUNE 2022
10
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
APPLICATION INFORMATION
Pressure Measurement
SGM621 is widely used in the application of bridge, such as measuring the pressure in weigh scales. It is also
suitable for detecting the pressure sensor with higher resistance due to high input impedance.
Figure 2 shows the pressure transducer bridge of 5kΩ which is powered by a 5V single supply. In such a circuit, the
bridge consumes only 1mA. The buffered voltage divider and SGM621 can condition the output signal with typical
3.3mA supply current.
The advantage of small size for SGM621 is attractive for the transducers of pressure. Because of the low noise and
drift, it can also be used in the application of diagnostic non-invasive blood pressure measurement.
Isolation Barrier
5V
4
3
5kΩ
5kΩ
5kΩ
5kΩ
+
G = 50
1kΩ
8
40kΩ
SGM621
2
1
+3.3V
7
REF
100Ω
445μA
TYP
6
_
AVDD DVDD
IN
100nF
ADC
20kΩ
+
STMS2
F407
40kΩ
_
1mA
MOSI
DVDD
SCK
AGND
SGM8581
CS
MISO
50μA
Figure 2. The Operation of the Pressure Monitor Circuit with 5V Single Supply
Medical ECG Amplifier
Because of the advantage of low current noise, SGM621 can be used in ECG monitors (Figure 3) where the source
resistances can reach 1MΩ or higher. It is the best choice to use SGM621 in the battery-powered data recorders as
it can operate on the condition of low supply voltage, low power and space-saving packages.
Moreover, for better performance, combining with the advantages of low voltage noise, low current and low bias
currents can enhance the dynamic range of SGM621.
The stability of the right leg drive loop can be maintained by the capacitor C1. Moreover, for protecting the patient
from the possible harm, the isolation safeguards should be added between the patient and the circuit part.
Isolation/Protection Barrier
+5V
4
R1
100kΩ
R4
5kΩ
3
C1
15pF
_
SGM8210-1
R5
1kΩ
+
R2
49.9kΩ
R3
SGM8210-1 49.9kΩ
+
RG
6.2kΩ
_
+
8
SGM621
G=9
2
1
7
_
0.03Hz
High-Pass
Filter
G = 111
Output
1V/mV
5
-5V
Reject the common voltage at the input of SGM621
Figure 3. The Circuit of Medical ECG Monitor
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JUNE 2022
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Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
APPLICATION INFORMATION (continued)
Precision V-I Converter
It’s easy to realize a precision current source (Figure 4)
utilizing one SGM621, another operational amplifier
and two resistors. To obtain a better CMRR of SGM621,
a buffer should be placed between the REF pin and the
OUT pin of the amplifier. The equation which is shown
in Figure 4 illustrates the output current of the circuit.
+VS
4
VIN+
3
+
8
SGM621
RG
2
1
VIN-
5
7
VSET
+
RSET
_
IL
+
SGM8581
-VS
IL =
VSET
=
RSET
_
RLOAD
[(VIN+) - (VIN-)]G
R1
Figure 4. Precision Voltage-to-Current Converter
Input and Output Offset Voltage
Two main sources which are error of input and output
result in the low errors of SGM621. When referred to
the input, the output error should be divided by the gain
of the instrumentation amplifier. From the equations
which are shown as below, the input error takes a
leading position at large gains while the output error
takes a leading position at small gains.
Total Error Referred to Input (RTI) = Input Error +
(Output Error/G)
Total Error Referred to Output (RTO) = (Input Error × G)
+ Output Error
Terminal of Reference
Potential of the reference terminal defines the zero
output voltage. It becomes extremely useful while the
load is not tied to the precise ground of the rest of the
system. The reference terminal provides one way to
bias a precise voltage to the output, and the reference
voltage should be in the range of 2V within the supply
voltages. On top of these, to keep better CMRR, the
parasitic resistor at this pin should be low.
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The gain of the instrumentation amplifier is determined
by the external resistor RG. The accuracy of the
external resistor RG is important as it may influence the
error of gain. It is recommended that selecting the
resistor with 0.1% or 1% precision is a good choice.
The following table shows the gain effect with the
selection of 1% or 0.1% precision resistor. Also, leaving
the pin 2 and pin 3 (the place of RG) open can make the
gain of SGM621 equals to 1.
49.4kΩ
G-1
RG =
6
_
Selection of Gain
As mentioned before, the gain error can be minimized
by equivalent parasitic resistor in series with RG.
Moreover, low TC of 1ppm/ ℃ is required for the
selection of RG to avoid the gain drift of SGM621.
Table 1. Different Values for Gain Resistor
1% STD
Table Value of
RG (Ω)
Calculated
Gain
0.1% STD
Table Value of
RG (Ω)
Calculated
Gain
49.9k
1.990
49.3k
2.002
12.4k
4.984
12.4k
4.984
5.49k
9.998
5.49k
9.998
2.61k
19.93
2.61k
19.93
1.00k
50.40
1.01k
49.91
499
100.0
499
100.0
249
199.4
249
199.4
100
495.0
98.8
501.0
49.9
991.0
49.3
1003.0
+VS
IN+
4
3
+
8
SGM621
RG
2
1
IN-
7
OUT
6
_
5
REF
-VS
Figure 5. Diode for Protecting VIN from Larger than VS
JUNE 2022
12
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
APPLICATION INFORMATION (continued)
RF Interference
One of the characteristics of instrumentation amplifier is
rectifying the small signal which is out of the band. This
kind of disturbance can be described as the small
biased voltage. All of the high frequency components
can be filtered by the R-C network which is placed in
the input position of the instrumentation amplifier, as
shown in Figure 6. The following equation shows the
equation of filtering frequency for the differential and
common mode part of the input signal.
FilterFreqDIFF =
1
2πR ( 2CD + CC )
1
2πRCC
FilterFreqCM =
CD ≥ 10CC is required in the above equation.
The capacitor CD influences the quality of the differential
signal, while CC influences the quality of the common
mode signal. The common mode rejection ratio would
be reduced if the R × CC is mismatched. To reduce this
negative influence and obtain a good CMRR, it is
recommended that the capacitance of CD should be 10
times larger than CC. To conclude, the larger the ratio of
CD:CC is, the less negative influence to the circuit.
Common Mode Rejection
The common mode rejection ratio of the instrumentation
amplifier is high as it can measure the differential signal
between the two inputs when both IN+ and IN- increase
or decrease equally. Also, this specification can be
defined in the whole range of input voltage.
To obtain a best CMRR, it is recommended that the
REF pin should be connected to a low impedance input
and the difference of impedance between two inputs
should be as small as possible. Also, using shielded
cable can effectively reduce the noise of the circuit, and
it should be driven properly for better value of CMRR.
The following two figures (Figure 7 and Figure 8)
illustrate the method to increase the CMRR for
alternating circuit by bootstrapping the capacitance of
the shielded cable, and this kind of method can also
reduce the mismatching of capacitance at the inputs.
+VS
+
RISO
49.9Ω
SGM8210-2
3
+
8
_
6
2
SGM8210-2
1
+
7 OUT
SGM621
RG
_
RISO
49.9Ω
+5V
IN+ 4
5
_
REF
IN-VS
100nF
10μF
Figure 7. Differential Input Shield Driving
CC
RFIRT
IN+
4
3
CD
+
8
+VS
IN+ 4
SGM621
RG
2
RFIRT
1
IN-
6
_
REF
5
RISO
50Ω
+
SGM8210-1
R1
49.9kΩ
R2
49.9kΩ
10μF
+
RG
499Ω
8
7 OUT
SGM621
2
_
CC
100nF
3
7 OUT
1
_
5
6
REF
IN-VS
-5V
Figure 8. Common Mode Input Shield Driving
Figure 6. One Method to Reduce the Interference of RF
SG Micro Corp
www.sg-micro.com
JUNE 2022
13
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
SGM621
APPLICATION INFORMATION (continued)
Isolation of Grounding
For solving the problems of grounding, REF pin should
be connected to the "local ground" as the output of the
instrumentation amplifier is biased with VREF.
Because of the noisy environment of the digital circuit,
the component of data-acquisition such as Analog
Digital Converter (ADC) has two pins which are AGND
and DGND. Also, the isolation can be made by using a
single line or 0Ω resistor. However, each returns of
ground should be separated so that the current flow
from the sensitive point could be minimized. Also, the
ground returns between analog and digital should be
tied together with one point, which is shown in ADC part
of Figure 9.
Digital
Power Supply
GND +3.3V
Analog
Power Supply
+10V GND -10V
100nF
100nF
4
+
100nF
+
8
-VCC
+VCC
5
7
SGM621
S/H
IN
AVDD
GND AVSS GND DVDD
ADC
OUT
To MCU
GND
_
1
100nF 100nF
6
Figure 9. Isolation of Grounding
Return of Grounding for IB
+VS
The bias current (IB) at the inputs is needed for
operating and biasing the transistor at the input stage of
the instrumentation amplifier, so it is also necessary to
design a ground return path for the bias current. For
example, for operating the floating inputs of the
amplifier (see Figure 10 ~ 12), such as AC-coupled
transformer, there should be an electrical line between
the input and the ground for ground return of bias
current.
3
+
2
IN-
_
7
OUT
6
2
_
1
IN-
5
REF
-VS
To the Ground of
Power Supply
8
7
SGM621
1
8
SGM621
RG
RFILT
10kΩ
RG
499Ω
+
3
Figure 11. Return of Grounding for IB with Thermocouple
Inputs
+VS
IN+ 4
IN+ 4
5
OUT
6
REF
-VS
IN+ 4
CFILT
AC
Coupled
3
Figure 10. Return of Grounding for IB with
Transformer-Coupled Inputs
RFILT
10kΩ
7
SGM621
RG
1
OUT
6
2
CFILT
To the Ground of
Power Supply
+
_
REF
INTo the Ground of
Power Supply
Figure 12. Return of Grounding for IB with AC-Coupled
Input
SG Micro Corp
www.sg-micro.com
JUNE 2022
14
SGM621
Low Power, Low Noise, Rail-to-Rail
Output, Instrumentation Amplifier
REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
JUNE 2022 ‒ REV.A.1 to REV.A.2
Page
Updated Terminal of Reference section ............................................................................................................................................................. 13
MARCH 2022 ‒ REV.A to REV.A.1
Page
Updated Electrical Characteristics section ........................................................................................................................................................... 5
Changes from Original (MARCH 2022) to REV.A
Page
Changed from product preview to production data ............................................................................................................................................. All
SG Micro Corp
www.sg-micro.com
JUNE 2022
15
PACKAGE INFORMATION
PACKAGE OUTLINE DIMENSIONS
SOIC-8
0.6
D
e
2.2
E
E1
5.2
b
1.27
RECOMMENDED LAND PATTERN (Unit: mm)
L
A
θ
A1
c
A2
Symbol
Dimensions
In Millimeters
MIN
MAX
Dimensions
In Inches
MIN
MAX
A
1.350
1.750
0.053
0.069
A1
0.100
0.250
0.004
0.010
A2
1.350
1.550
0.053
0.061
b
0.330
0.510
0.013
0.020
c
0.170
0.250
0.006
0.010
D
4.700
5.100
0.185
0.200
E
3.800
4.000
0.150
0.157
E1
5.800
6.200
0.228
0.244
e
1.27 BSC
0.050 BSC
L
0.400
1.270
0.016
0.050
θ
0°
8°
0°
8°
NOTES:
1. Body dimensions do not include mode flash or protrusion.
2. This drawing is subject to change without notice.
SG Micro Corp
www.sg-micro.com
TX00010.000
PACKAGE INFORMATION
PACKAGE OUTLINE DIMENSIONS
MSOP-8
b
E1
E
4.8
1.02
e
0.41
0.65
RECOMMENDED LAND PATTERN (Unit: mm)
D
L
A
c
A1
θ
A2
Symbol
Dimensions
In Millimeters
MIN
MAX
Dimensions
In Inches
MIN
MAX
A
0.820
1.100
0.032
0.043
A1
0.020
0.150
0.001
0.006
A2
0.750
0.950
0.030
0.037
b
0.250
0.380
0.010
0.015
c
0.090
0.230
0.004
0.009
D
2.900
3.100
0.114
0.122
E
2.900
3.100
0.114
0.122
E1
4.750
5.050
0.187
e
0.650 BSC
0.199
0.026 BSC
L
0.400
0.800
0.016
0.031
θ
0°
6°
0°
6°
NOTES:
1. Body dimensions do not include mode flash or protrusion.
2. This drawing is subject to change without notice.
SG Micro Corp
www.sg-micro.com
TX00014.000
PACKAGE INFORMATION
TAPE AND REEL INFORMATION
REEL DIMENSIONS
TAPE DIMENSIONS
P2
W
P0
Q1
Q2
Q1
Q2
Q1
Q2
Q3
Q4
Q3
Q4
Q3
Q4
B0
Reel Diameter
A0
P1
K0
Reel Width (W1)
DIRECTION OF FEED
NOTE: The picture is only for reference. Please make the object as the standard.
KEY PARAMETER LIST OF TAPE AND REEL
Reel
Diameter
Reel Width
W1
(mm)
A0
(mm)
B0
(mm)
K0
(mm)
P0
(mm)
P1
(mm)
P2
(mm)
W
(mm)
Pin1
Quadrant
SOIC-8
13″
12.4
6.40
5.40
2.10
4.0
8.0
2.0
12.0
Q1
MSOP-8
13″
12.4
5.20
3.30
1.50
4.0
8.0
2.0
12.0
Q1
SG Micro Corp
www.sg-micro.com
TX10000.000
DD0001
Package Type
PACKAGE INFORMATION
CARTON BOX DIMENSIONS
NOTE: The picture is only for reference. Please make the object as the standard.
KEY PARAMETER LIST OF CARTON BOX
Length
(mm)
Width
(mm)
Height
(mm)
Pizza/Carton
13″
386
280
370
5
SG Micro Corp
www.sg-micro.com
DD0002
Reel Type
TX20000.000
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