AME AM467

Precision amplifier for bridge circuits
AM467
PRINCIPLE FUNCTION
Adjustable amplification of differential input voltage signals
(from 0 to ±5 mV FS up to 0 to ±100 mV FS)
to an adjustable, ratiometric output voltage of 0.2V to Vcc-0.2 V
_ 5%
VCC = 5V+
Differential
input
voltages
_ 5...+
_ 100mV FS)
(+
AM467
VOUT =0,2...VCC -0,2V
(adjustable)
e.g.0,5...4,5V
ratiometric
TYPICAL APPLICATIONS
•
•
•
•
Amplifiers for ceramic sensing elements
Amplifiers for DMS sensing elements
Amplifiers for GMR sensing elements
For industrial and automotive applications
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
February 2007
1/9
Rev. 1.0
Precision amplifier for bridge circuits
AM467
TABLE OF CONTENTS
PRINCIPLE FUNCTION
1
TYPICAL APPLICATIONS
1
FEATURES
3
GENERAL DESCRIPTION
3
BLOCK DIAGRAM
3
ELECTRICAL SPECIFICATIONS
4
DESCRIPTION OF FUNCTIONS
5
EXAMPLE APPLICATION
5
The procedure in detail (for calibration with discrete resistors)
DIMENSIONING
6
7
NOTES
8
BLOCK DIAGRAM and PINOUT
8
FURTHER READING
9
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
February 2007
2/9
Rev. 1.0
Precision amplifier for bridge circuits
AM467
FEATURES
GENERAL DESCRIPTION
• Wide differential input voltage range
(±5 mV FS...±100 mV FS)
• Low offset
• Low offset drift
• Low input noise
• High CMRR: > 120 dB
• Wide operating temperature range:
– 40 °C... +125 °C
• Adjustable output voltage
• Rail-to-rail output stage:
VOUT = 0.2 V ... VCC – 0.2 V
• Sink/source output
• Single ratiometric supply: VCC = 5 V
• Integrated EMV protective functions
• Overvoltage protection 12 V
• Integrated ESD protective functions
• Short-circuit-proofing
• Small-scale design
AM457 is a high-precision integrated amplifier
which has been developed to condition signals
from small differential input voltages within a
range of a few millivolts (±5 to ±100 mV FS).
The chief component of the IC is a highly
accurate, low-noise amplifier circuit which can
be adjusted to the sensing elements using an
external network of resistors.
With the exception of the additional operational
amplifier and the diagnostic unit IC AM467's
pins and functions are compatible with the
AM457.
The rail-to-rail output makes the IC suitable for
the amplification of DMS and piezoceramic
sensing elements and GMR measuring cells with
respect to the specific calibration network.
BLOCK DIAGRAM
VCC
8
AM467
IN- 2
IN+ 3
Inputamplifier
Biasing
Unit
Output
stage
1 OUT
Short circuit
protection
Current limitation
4
GND
Figure 1: Block diagram for AM467
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
February 2007
3/9
Rev. 1.0
Precision amplifier for bridge circuits
AM467
ELECTRICAL SPECIFICATIONS
(with reference to the example application)
Tamb = 25°C, VCC = 5V (unless otherwise stated)
Parameter
Symbol
Voltage Range
VCC
Quiescent Current
ICC
Conditions
Tamb = – 40 ... +125°C
Min.
Typ.
Max.
Unit
4.5
5
5.5
V
170
320
530
µA
°C
Temperature Specifications
Operating
Tamb
–45
125
Storage
Tst
–55
150
°C
Junction
TJ
150
°C
±0.1
±0.3
mV
±0.5
±3
µV/°C
±6
µV/°C
Amplifier AMP
Offset Voltage
VOS
VOS vs. Temperature
dVOS/dT
Tamb= -45 … 105°C
VOS vs. Temperature
dVOS/dT
Tamb= 105 … 125°C
Input Bias Current
IB
VCM = 2.5V
IB vs. Temperature
dIB/dT
Tamb= -45…125°C
30
200
nA
–0.13
–0.6
nA/°C
Differential Input Voltage
VIN
VIN =Vout+ – Vout-
±100
mV
Input Offset Current
IOS
VCM = 2.5V
IOS vs. Temperature
dIOS/dT
Tamb= -45 … 125°C
±0.5
±5
nA
Input Resistance
RIN
VCM / IB,typ (VCM = 2.5V)
±2.5
±30
pA/°C
Input Capacitance
CIN
By design
Common Mode Input Range
CMIR
1
Common Mode Rejection Ratio
CMRR
100
120
dB
Open Loop Gain
G0
120
140
dB
Adjustable Gain
G
Output Voltage Range
VOUT
Guaranteed Max Output Current
IOUT
Sink and source
250
µA
Output Load Resistance
RL
= VOUT / I OUT , sink and source
20
kΩ
Power Supply Rejection Ratio
PSRR
90
110
dB
Gain Bandwidth Product
GBW
R1,2=1k Rk=10k, C1=1nF,
Ck=100pF, no RL
190
310
kHz
±5
See Figure 2
Non Linearity
80
MΩ
90
C1 = 1nF; Iout = 1µA
pF
3.7
V
10
0.2
VCC – 0.2
10-4
NL = G/Go, G ≤ 100
Slew Rate
SR
C1 = 1nF; RL = 20kΩ
Input Voltage Noise
en
Rs = 100Ω; VCC = 5V ; fg=1kHz
with Rs = Source Impedance
V
0.2
0.3
13.5
Overvoltage Protection
V/µs
20
nV/√Hz
12
V
Table 1: Specifications
Currents flowing into the IC are negative. VCM = Input Common Mode Voltage
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
February 2007
4/9
Rev. 1.0
Precision amplifier for bridge circuits
AM467
EXTERNAL COMPONENTS
Parameter
Symbol
Conditions
Min.
Typ.
1
Max.
Output Capacitor
C1
Compensation Capacitor
C2
100
pF
Stabilization Capacitor (optional)
C3
100
nF
EMV Protection Capacitor (optional)
C4
470
pF
Load Resistor to GND, to VCC
RL
Vout = max. Vout
5
Unit
20
nF
kΩ
Table 2: External components of the calibration network
Recommended: ceramic capacitors
DESCRIPTION OF FUNCTIONS
AM457 is an integrated precision circuit for the signal amplification of high-impedance signal
sources and for the signal conditioning of sensor bridges with low sensitivity, particularly for
ceramic and DMS sensing elements or GMR measuring cells.
The IC generates a rail-to-rail output signal of 0.2 V to Vcc-0.2 V. The amplification and offset can
be set independently of one another using external resistors. Through the suitable dimensioning of
external resistors in particular an output voltage of 0.5...4.5 V can also be provided. As these values
are standard the following description refers to this output voltage.
AM467 works on the principle of ratiometry with a supply voltage of 5 V ±5%. The IC is
distinguished by its low offset and extremely low thermal offset drift across a wide temperature
range, enabling it to be classified as a precision amplifier.
The sink and source output stage is protected internally against short-circuiting.
The AM467 design incorporates protective measures against interference from EMV and ESD
using suitable semiconductor structures.
With the exception of the additional operational amplifier and the diagnostic unit the IC is
compatible with AM457. AM467 thus has a smaller chip surface and a lower power consumption.
AM467 can be used as an autonomous signal conditioning IC or as a preamplifier for an A/D
converter for back-end digitization.
EXAMPLE APPLICATION
AM457 is suitable for the amplification of resistance networks connected up as a Wheatstone
bridge with four resistors and which have a low sensitivity, such as 1.0 to 3.5 mV/V with a 5 V
supply, for example. By way of example a sensor application is described herein which is
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
February 2007
5/9
Rev. 1.0
Precision amplifier for bridge circuits
AM467
based on a piezoceramic sensing element such as the above and is to be calibrated to an output
signal of 0.5...4.5 V (sensor system).
The basic calibration procedure
The sensor system is calibrated in two stages. Using a mathematical algorithm (Excel sheet:
Cali_AM467_rev1.xls) and taking AM467's measured output voltage values and the individual
sensor bridge values as a basis, the values for the two resistors (calibration resistors) are calculated.
In the calibration of the system all effective errors (parasitic effects and component tolerances) are
taken into account.
The sensing element is first measured and secondly the electrical characteristics of the sensor using
predefined precision measuring resistors. This information is then processed in an Excel program to
calculate the setpoint for two of the calibration resistors which are then swapped with the given
measuring resistors and added to the circuit accordingly.
If necessary, in a second stage the offset of the output voltage can be corrected using the
information given in the Excel sheet.
The procedure in detail (for calibration with discrete resistors)
In order to evaluate the sensor system signal four resistors (R1 to R4) are required (see Figure 2).
The values of the two resistors R2 and R4 are fixed for the network and do not have to be adjusted
during calibration. Like capacitors C1 to C4 they can be mounted on the circuit board at the outset.
Resistors R1 and R3 act as measuring resistors and are assembled on the measuring apparatus for all
sensor systems in one sensing element category (see Dimensioning). Their values must be as close
as possible to those calculated by Analog Microelectronics for the relevant sensing element
category. With the described components (R1 to R4 and C1 to C4) the sensor signal is at its operating
point which then enables calibration.
For this purpose a few of the electrical characteristics of the sensing element are first determined
without the evaluation circuitry being connected (Stage 1). Using the Excel calibration software
(Kali_AM467.xls) the necessary calibration parameters are: the sensing element resistance (RBR),
average output voltage of the sensing element (VBR) and the system's supply voltage (VCC).
Once these three values have been determined the sensing element is connected up to the evaluation
circuit. The output signal at the AM467 IC (Out1 and Out2) is measured at zero and full pressure
(offset and full scale signal) and entered into the Excel program with the bridge values including the
values for the given maximum pressure of the sensing element (Pmax).
Taking these values and applying them to a calibration algorithm the two resistors R1 and R3 are
calculated separately for each individual system. These then replace the measuring resistors and
have to be soldered onto the circuit board.
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
February 2007
6/9
Rev. 1.0
Precision amplifier for bridge circuits
AM467
Resistors R1 and R3 are described as calibration resistors. These stipulate the final operating point.
Once these resistors have been mounted the calibration procedure is complete. Depending on the
accuracy of the resistors used an offset value of 0.5 V and a full scale signal of 4.5 V should have
been obtained.
Should the expected final accuracy require it, in an additional second stage (Stage 2) the offset of
the output voltage can be corrected using resistor R1. To this end the AM467 output must again be
measured at P = 0 bar. If at 0 bar the output is too high or too low by a few millivolts, for example,
the Excel program then calculates the necessary second correction of R1 in ohms.
The offset error which is then obtained if a different resistance is used in place of calculated
resistance R1 can also be determined by the Excel sheet. The sensitivity in mV/ohm is instrumental
here, providing information as to by how many millivolts the offset shifts when the used resistor R1
has a delta R (in ohms) to the calculated value. The given sensitivity value (mV/ohm) is multiplied
by the delta R of resistor R1 to obtain a change in offset which affects both the offset (0.5 V) and the
full scale signal (4.5 V).
AM467
8
VCC
R3
C1
IN+
C4
IN-
3
AMP
2
Output stage
with short
circuit proofing
1
R1
OUT
R2
4
C2
Vout
C3
R4
GND
GND
Figure 3: Ceramic sensing element with AM467 and a calibration network
with external resistors.
DIMENSIONING
In the combination of ceramic sensing element and AM467 the operating point (the initial value of
the four resistors R1 to R4) was determined for all sensing elements in a specific sensing element
category. In the case of piezoceramic sensors the term "sensing element category" is used to denote
sensing elements with the following characteristics:
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
February 2007
7/9
Rev. 1.0
Precision amplifier for bridge circuits
AM467
Bridge resistance: 11 kOhm ± 20%
Sensitivity: 2.4 ± 1 mV/V
Offset: 0 to ± 0.3 mV/V
Supply voltage: 5 V ± 10%
The following values are obtained for the above sensing element categories:
Fixed resistor R2 = 33 k; accuracy of 1%
Fixed resistor R4 = 12 k; accuracy of 1%
Measuring resistor R1 = 11 k; accuracy of 0.1%
Measuring resistor R3 = 120 k; accuracy of 0.1%
C1 = 100 nF (optional)
C2 = 100 pF (ceramic)
C3 = 1 nF to 5 nF (ceramic)
C4 = 470 pF optional (ceramic)
NOTES
For bridge circuits with characteristics other than the above (with other sensing element categories,
such as DMS sensing elements, for example) Analog Microelectronics can adapt the dimensioning
program on request.
An Excel program (Cali_AM467_rev1.xls) is used for calibration (the calculation of the definitive
operating point). This is available on the www.analogmicro.de website.
DIAGRAM and PINOUT
AM467
8 VCC
IN+ 3
+
2
-
IN-
AMP
Output stage
with short
circuit proofing
1 OUT
OUT
ININ+
GND
1
2
3
4
8
7
6
5
VCC
N.C.
N.C.
N.C.
4
Figure 4: AM467 Pinout
GND
Figure 3: Diagram of AM467
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
February 2007
8/9
Rev. 1.0
Precision amplifier for bridge circuits
AM467
PIN
1
2
3
4
5
6
7
8
NAME
OUT
ININ+
GND
N.C.
N.C.
N.C.
VCC
EXPLANATION
Output
Negative Input
Positive Input
IC Ground
No function
No function
No function
5V Supply Voltage
Table 3: Pin configuration for AM467
For package dimensions see: http://www.analogmicro.de/products/analogmicro.de.en.package.pdf
FURTHER READING
As AM467 is identical in its specifications to AM457 – with the exception of the diagnosis – the
calibration guidelines given for the latter also apply to AM467, available at www.analogmicro.de
for various different networks.
AN1009 Application description
AN1011 Calibration for DMS sensing elements
AN1012 Calibration for piezoceramic sensing elements
DELIVERY OPTIONS
AM467 is available as:
• An SOP 8
• Dice in a 4" wafer on 5" blue foil (on request)
NOTES
Analog Microelectronics reserves the right to make amendments to dimensions, technical data and any other
information without prior notice.
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: http://www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
February 2007
9/9
Rev. 1.0