SGM620

Low Power, Low Noise, Rail-to-Rail Output, Instrumentation Amplifier

ADVANCED DATASHEET

SG Micro Corp www.sg-micro.com

OCTOBER 19, 2018

GENERAL DESCRIPTION The SGM620 is a high accuracy instrumentation amplifier that requires only one external resistor to set gains of 1 to 10000. Furthermore, the SGM620 features SOIC-8 package that is smaller than discrete designs and offers lower power (only 1mA (TYP) supply current), making it a good fit for battery-powered, portable (or remote) applications.

The SGM620, with its high accuracy of 10ppm (TYP) non-linearity and low offset voltage of 80μV (TYP) is ideal for use in precision data acquisition systems, such as weigh scales and transducer interfaces. Furthermore, the low noise, low input bias current and low power of the SGM620 make it well suited for medical applications, such as ECG and non-invasive blood pressure monitors.

The SGM620 works well as a pre-amplifier due to its low input voltage noise of 13nV/ zH at 1kHz, 0.22μVP-P in the 0.1Hz to 10Hz band and 60fA/ zH input current noise. Also, the SGM620 is well suited for multiplexed applications with its settling time of 19μs to 0.01%.

The SGM620 is available in Green SOIC-8 package. It is specified over the extended -40 ℃ to +125 ℃ temperature range.

FEATURES ● Rail-to-Rail Output ● Easy to Use

Gain Set with One External Resistor (Gain Range 1 to 10000) Support Single or Dual Power Supplies: 3.6V to 36V or ±1.8V to ±18V Higher Performance than 3 Operational Amplifier IA Designs Low Power, Supply Current: 1mA (TYP)

● Excellent DC Performance Input Offset Voltage: 80μV (TYP) Input Bias Current: 0.8nA (TYP) Common Mode Rejection Ratio: 96dB (TYP) (G = 10)

● Low Noise Input Voltage Noise: 13nV/ zH at 1kHz 0.1Hz to 10Hz Voltage Noise: 0.22μVP-P

● Excellent AC Specifications Bandwidth: 65kHz (G = 100) Settling Time to 0.01%: 19μs (G = 100)

● -40℃ to +125℃ Operating Temperature Range ● Available in Green SOIC-8 Package APPLICATIONS Weigh Scales ECG and Medical Instrumentation Transducer Interfaces Data Acquisition Systems Industrial Process Controls

Low Power, Low Noise, Rail-to-Rail SGM620 Output, Instrumentation Amplifier

2 OCTOBER 2018 SG Micro Corp

www.sg-micro.com

PACKAGE/ORDERING INFORMATION

MODEL PACKAGE DESCRIPTION

SPECIFIED TEMPERATURE

RANGE ORDERING NUMBER

PACKAGE MARKING

PACKING OPTION

SGM620 SOIC-8 -40℃ to +125℃ SGM620XS8G/TR SGM

620XS8 XXXXX

Tape and Reel, 4000

MARKING INFORMATION XXXXX = Date Code, Trace Code and Vendor Code.

Trace Code Vendor Code

Date Code - Year

X XXX X

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 ............................................................... ±18V Input Common Mode Voltage .......................................... ±VS Junction Temperature ................................................. +150℃ Storage Temperature Range ........................ -65℃ to +150℃ Lead Temperature (Soldering, 10s) ............................ +260℃ RECOMMENDED OPERATING CONDITIONS Operating Temperature Range ..................... -40℃ to +125℃

PIN CONFIGURATION (TOP VIEW)

RG

OUT

REF

RG1

2

3

4

-IN

+IN

-VS

+VS

5

6

7

8

+

_

SOIC-8

OVERSTRESS CAUTION 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. ESD SENSITIVITY CAUTION This integrated circuit can be damaged by ESD if you don’t pay attention to ESD protection. 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 very small parametric changes could cause the device not to meet its published specifications. DISCLAIMER SG Micro Corp reserves the right to make any change in circuit design, or specifications without prior notice.

Low Power, Low Noise, Rail-to-Rail SGM620 Output, Instrumentation Amplifier

3 OCTOBER 2018 SG Micro Corp

www.sg-micro.com

ELECTRICAL CHARACTERISTICS (At TA = +25℃, VS = ±15V, RL = 2kΩ, unless otherwise noted.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

INPUT CHARACTERISTICS

Input Bias Current IB 0.8 nA

Input Offset Current IOS 0.4 nA

Common Mode Rejection Ratio with 1kΩ Source Imbalance

G = 1

CMRR

VCM = -10V to +10V 77

dB G = 10 VCM = -10V to +10V 96

G = 100 VCM = -10V to +10V 115

G = 1000 VCM = -10V to +10V 130

VOLTAGE OFFSET (Total RTI Error = VOSI + VOSO/G)

Input Offset Voltage VOSI 80 µV

Output Offset Voltage VOSO 100

Offset Referred to the Input vs. Supply

G = 1

PSRR

VS = ±2.3V to ±18V 126

dB G = 10 VS = ±2.3V to ±18V 146

G = 100 VS = ±2.3V to ±18V 160

G = 1000 VS = ±2.3V to ±18V 160

REFERENCE INPUT

Reference Input Resistance RREF 20 kΩ

Reference Input Current IREF VIN+, VREF = 0 40 µA

OUTPUT CHARACTERISTICS

Output Voltage Swing

VOH RL = 10kΩ 0.25

V RL = 2kΩ 0.75

VOL RL = 10kΩ 0.13

RL = 2kΩ 0.4

Short-Circuit Current ISOURCE 20

mA ISINK 26

POWER SUPPLY

Quiescent Current IQ IOUT = 0 1 mA

GAIN (G = 1 + (49.4kΩ/RG))

Gain Range 1 10000

Gain Error (1)

G = 1

ErrGain

VOUT = ±10V 0.01

% G = 10 VOUT = ±10V 3.5

G = 100 VOUT = ±10V 4

G = 1000 VOUT = ±10V 4

Non-Linearity

G = 1

NonLGain

VOUT = -10V to +10V 3

ppm G = 10 VOUT = -10V to +10V 4

G = 100 VOUT = -10V to +10V 5

G = 1000 VOUT = -10V to +10V 10 NOTE: (1) Does not include effects of external resistor RG.

Low Power, Low Noise, Rail-to-Rail SGM620 Output, Instrumentation Amplifier

4 OCTOBER 2018 SG Micro Corp

www.sg-micro.com

ELECTRICAL CHARACTERISTICS (continued) (At TA = +25℃, VS = ±15V, RL = 2kΩ, unless otherwise noted.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

DYNAMIC RESPONSE

Small-Signal -3dB Bandwidth

G = 1

3900

kHz G = 10 500

G = 100 65

G = 1000 6.5

Slew Rate SR VOUT = 1VP-P step, G = 1 1.1 V/µs

Settling Time to 0.01%

G = 1

tS

10V step 12

µs G = 10 10V step 7

G = 100 10V step 19

G = 1000 10V step 150

NOISE

Input Voltage Noise Density eni f = 1kHz 13 nV/ zH

Output Voltage Noise Density eno f = 1kHz 70

0.1Hz to 10Hz Voltage Noise, RTI

G = 1

f = 0.1Hz to 10Hz 4

µVP-P G = 10 f = 0.1Hz to 10Hz 0.49

G = 100 f = 0.1Hz to 10Hz 0.35

G = 1000 f = 0.1Hz to 10Hz 0.22

Current Noise Density , RTI f = 1kHz 60 fA/ zH

0.1Hz to 10Hz Current Noise f = 0.1Hz to 10Hz 18 pAP-P

Low Power, Low Noise, Rail-to-Rail SGM620 Output, Instrumentation Amplifier

5 OCTOBER 2018 SG Micro Corp

www.sg-micro.com

THEORY OF OPERATION The SGM620 is a monolithic instrumentation amplifier based on a modification of the classic three operational amplifier approach.

-INR3

400Ω

Q1

I1 20μA 20μA I2VB

C1 C2

R1 R2

Q2

RG

+- + -

+

-

A1 A2

A3

GainSense

GainSense

R4400Ω

10kΩ

10kΩ

10kΩ

10kΩ

+IN

REF

OUT

-VS

+VS

+VS +VS

Figure 1. Simplified Schematic of SGM620 The input transistors Q1 and Q2 provide a single differential pair input for high precision (Figure 1), yet offer 10 × lower input bias current. Feedback through the Q1-A1-R1 loop and the Q2-A2-R2 loop maintains constant collector current of the input devices Q1 and Q2, thereby impressing the input voltage across the external gain setting resistor RG. This creates a differential gain from the inputs to the A1/A2 outputs given by G = (R1 + R2)/RG + 1. The unity-gain subtractor, A3, removes any common mode signal, yielding a single-ended output referred to the REF pin potential.

The value of RG also determines the transconductance of the pre-amp stage. As RG is reduced for larger gains, the transconductance increases asymptotically to that of the input transistors. This has three important advantages:

(a) Open-loop gain is boosted for increasing programmed gain, thus reducing gain related errors.

(b) The gain-bandwidth product (determined by C1 and C2 and the pre-amp transconductance) increases with programmed gain, thus optimizing frequency response. (c) The input voltage noise is reduced to a value of 13nV/ zH , determined mainly by the collector current and base resistance of the input devices.

The internal gain resistors, R1 and R2, are trimmed to an absolute value of 24.7kΩ, allowing the gain to be programmed accurately with a single external resistor.

The gain equation is then

G

49.4kΩG = + 1R

G49.4kΩR = G - 1

Low Power, Low Noise, Rail-to-Rail SGM620 Output, Instrumentation Amplifier

6 OCTOBER 2018 SG Micro Corp

www.sg-micro.com

APPLICATION INFORMATION

+

SGM6203kΩ

3kΩ3kΩ

3kΩ

5V

1.7mA1mATYP

0.1mA

G = 100499Ω

20kΩ

10kΩ

20kΩ

+

_

0.6mATYP

REFIN

AGND

DigitalDataOutput

ADC

_

38

12

4

5

6

7

Figure 2. A Pressure Monitor Circuit that Operates on a 5V Single Supply

Pressure Measurement Although useful in many bridge applications, such as weigh scales, the SGM620 is especially suitable for higher resistance pressure sensors powered at lower voltages where small size and low power become more significant.

Figure 2 shows a 3kΩ pressure transducer bridge powered from 5V. In such a circuit, the bridge consumes only 1.7mA. Adding the SGM620 and a buffered voltage divider allows the signal to be conditioned for 3.3mA (TYP) of total supply current.

Small size makes the SGM620 especially attractive for voltage output pressure transducers. Since it delivers low noise and drift, it will also serve applications such as diagnostic non-invasive blood pressure measurement.

Medical ECG Amplifier The low current noise of the SGM620 allows its use in ECG monitors (Figure 3) where high source resistances of 1MΩ or higher are not uncommon. The SGM620’s low power, low supply voltage requirements, and space-saving SOIC-8 package offering make it an excellent choice for battery powered data recorders.

Furthermore, the low bias currents and low current noise, coupled with the low voltage noise of the SGM620, improve the dynamic range for better performance.

The value of capacitor C1 is chosen to maintain stability of the right leg drive loop. Proper safeguards, such as isolation, must be added to this circuit to protect the patient from possible harm.

SGM620

7

RG8.25kΩ

R324.9kΩR224.9kΩ

+

-

0.03hzHigh-Pass

FilterG = 143

Patient/CircuitProtection/Isolation

C1R1

10kΩ

R41MΩ

G = 7Output

Amplifier

OUTPUT1V/mV

+3V

-3V

+

_

3

8

1

2

4

5

6

Figure 3. A Medical ECG Monitor Circuit

Low Power, Low Noise, Rail-to-Rail SGM620 Output, Instrumentation Amplifier

7 OCTOBER 2018 SG Micro Corp

www.sg-micro.com

APPLICATION INFORMATION (continued) Precision V-I Converter The SGM620, along with another operational amplifier and two resistors, makes a precision current source (Figure 4). The operational amplifier buffers the reference terminal to maintain good CMR. The output voltage, VX, of the SGM620 appears across R1, which converts it to a current. This current, less only the input bias current of the operational amplifier, then flows out to the load.

SGM620RG

Load

VIN+

VIN-

+VS

+VX-

R1

IL

IL = VXR1

= [(VIN+) - (VIN-)]GR1

+

_

+

_

38

12

4

5

6

7

Figure 4. Precision Voltage-to-Current Converter

(Operates on 1.8mA, ±3V) Input and Output Offset Voltage The low errors of the SGM620 are attributed to two sources, input and output errors. The output error is divided by G when referred to the input. In practice, the input errors dominate at high gains, and the output errors dominate at low gains. The total VOS for a given gain is calculated as

Total Error RTI = Input Error + (Output Error/G) Total Error RTO = (Input Error × G) + Output Error Reference Terminal The reference terminal potential defines the zero output voltage and is especially useful when the load does not share a precise ground with the rest of the system. It provides a direct means of injecting a precise offset to the output, with an allowable range of 2V within the supply voltages. Parasitic resistance should be kept to a minimum for optimum CMR.

Gain Selection The SGM620’s gain is resistor-programmed by RG, or more precisely, by whatever impedance appears between Pins 1 and 8. The SGM620 is designed to offer accurate gains using 0.1% to 1% resistors. Table 1 shows required values of RG for various gains. Note that for G = 1, the RG pins are unconnected (RG = ∞). For any arbitrary gain, RG can be calculated by using the formula:

G49.4kΩR = G - 1

To minimize gain error, avoid high parasitic resistance in series with RG; to minimize gain drift, RG should have a low TC — less than 10ppm/℃ — for the best performance. Table 1. Required Values of Gain Resistors

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

REF

SGM620

R

R

VOUT

+IN

-IN

+SUPPLY

-SUPPLY

+

_

Figure 5. Diode Protection for Voltages beyond Supply

Low Power, Low Noise, Rail-to-Rail SGM620 Output, Instrumentation Amplifier

8 OCTOBER 2018 SG Micro Corp

www.sg-micro.com

APPLICATION INFORMATION (continued) RF Interference All instrumentation amplifiers rectify small out of band signals. The disturbance may appear as a small DC voltage offset. High frequency signals can be filtered with a low pass R-C network placed at the input of the instrumentation amplifier. Figure 6 demonstrates such a configuration. The filter limits the input signal according to the following relationship:

( )DIFFD C

1FilterFreq = 2πR 2C + C

CMC

1FilterFreq = 2πRC

where CD ≥ 10CC.

CD affects the difference signal. CC affects the common mode signal. Any mismatch in R × CC will degrade the SGM620’s CMRR. To avoid inadvertently reducing CMRR-bandwidth performance, make sure that CC is at least one magnitude smaller than CD. The effect of mismatched CCs is reduced with a larger CD:CC ratio.

SGM620499Ω

R

R

CC

CC

CD

+IN

-IN

0.1μF 10μF

10μF0.1μF

REF

VOUT

+15V

-15V

+

_

Figure 6. Circuit to Attenuate RF Interference

Common Mode Rejection Instrumentation amplifiers, such as the SGM620, offer high CMR, which is a measure of the change in output voltage when both inputs are changed by equal amounts. These specifications are usually given for a full-range input voltage change and a specified source imbalance.

For optimal CMR, the reference terminal should be tied to a low impedance point, and differences in capacitance and resistance should be kept to a minimum between the two inputs. In many applications, shielded cables are used to minimize noise; for best CMR over frequency, the shield should be properly driven. Figure 7 and Figure 8 show active data guards that are configured to improve AC common mode rejections by “bootstrapping” the capacitances of input cable shields, thus minimizing the capacitance mismatch between the inputs.

SGM620RG

+VS

-INPUT

+INPUT

100Ω

100Ω

REFERENCE

VOUT

-VS

-VS

+

_

+_

2

1

8

34

5

6

7

_

+

Figure 7. Differential Shield Driver

SGM620RG/2

+VS

-INPUT

+INPUT

100Ω

REFERENCE

VOUT

RG/2

-VS

+

_

+

_2

1

8

34

5

6

7

Figure 8. Common Mode Shield Driver

Low Power, Low Noise, Rail-to-Rail SGM620 Output, Instrumentation Amplifier

9 OCTOBER 2018 SG Micro Corp

www.sg-micro.com

APPLICATION INFORMATION (continued) Grounding Since the SGM620 output voltage is developed with respect to the potential on the reference terminal, it can solve many grounding problems by simply tying the REF pin to the appropriate “local ground”.

To isolate low level analog signals from a noisy digital environment, many data-acquisition components have separate analog and digital ground pins (Figure 9). It would be convenient to use a single ground line; however, current through ground wires and PC runs of the circuit card can cause hundreds of millivolts of error. Therefore, separate ground returns should be provided to minimize the current flow from the sensitive points to

the system ground. These ground returns must be tied together at some point, usually best at the ADC package shown in Figure 9. Ground Returns for Input Bias Currents Input bias currents are those currents necessary to bias the input transistors of an amplifier. There must be a direct return path for these currents. Therefore, when amplifying “floating” input sources, such as transformers or ac-coupled sources, there must be a DC path from each input to ground, as shown in Figure 10, Figure 11 and Figure 12.

SGM620 S/H ADC

2

3

7

46

5OUT

+VCC -VCC

ANALOG P.S.+15V -15VC

DIGITAL P.S.C +5V

0.1µF 0.1µF 1µF 1µF 1µF

DigitalDataOutput

+

+

_

Figure 9. Basic Grounding Practice

SGM620RG

LOAD

+VS

-INPUT

+INPUT

REFERENCE

VOUT

To PowerSupplyGround

-VS

1

8

3 4

7

6

5

2

Figure 10. Ground Returns for Bias Currents with Transformer-Coupled Inputs

SGM620

7

RG

LOAD

+VS

-INPUT

+INPUTREFERENCE

VOUT

To PowerSupplyGround

-VS

2

1

3 4

8 5

6

Figure 11. Ground Returns for Bias Currents with Thermocouple Inputs

SGM620RG

LOAD

+VS

REFERENCE

VOUT

To PowerSupply

Ground

100kΩ100kΩ-VS

-INPUT

+INPUT

2

1

8

3 4

5

6

7

Figure 12. Ground Returns for Bias Currents with AC-Coupled Inputs

PACKAGE INFORMATION

TX00010.000 SG Micro Corp www.sg-micro.com

PACKAGE OUTLINE DIMENSIONS SOIC-8

Symbol Dimensions

In Millimeters Dimensions

In Inches MIN MAX 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°

D

EE1

e

b

A

A2

A1 c

L

θ

1.27

0.6

2.2

5.2

RECOMMENDED LAND PATTERN (Unit: mm)

PACKAGE INFORMATION

TX10000.000 SG Micro Corp

www.sg-micro.com

TAPE AND REEL INFORMATION NOTE: The picture is only for reference. Please make the object as the standard.

KEY PARAMETER LIST OF TAPE AND REEL

Package Type Reel Diameter

Reel Width W1

(mm) A0

(mm) B0

(mm) K0

(mm) P0

(mm) P1

(mm) P2

(mm) W

(mm) Pin1

Quadrant

DD0001 SOIC-8 13″ 12.4 6.40 5.40 2.10 4.0 8.0 2.0 12.0 Q1

Reel Width (W1)

Reel Diameter

REEL DIMENSIONS

TAPE DIMENSIONS

DIRECTION OF FEED

P2 P0

W

P1 A0 K0

B0Q1 Q2

Q4Q3 Q3 Q4

Q2Q1

Q3 Q4

Q2Q1

PACKAGE INFORMATION

TX20000.000 SG Micro Corp

www.sg-micro.com

CARTON BOX DIMENSIONS NOTE: The picture is only for reference. Please make the object as the standard.

KEY PARAMETER LIST OF CARTON BOX

Reel Type Length (mm)

Width (mm)

Height (mm) Pizza/Carton

DD0002 13″ 386 280 370 5