Datasheet
15
LT1167
Figure 6. “Roll Your Own” vs LT1167
“ROLL YOUR OWN”’ CIRCUIT
ERROR SOURCE LT1167C CIRCUIT CALCULATION CALCULATION LT1167C “ROLL YOUR OWN”
Absolute Accuracy at T
A
= 25
°
C
Input Offset Voltage, µV60µV/20mV 100µV/20mV 3000 5000
Output Offset Voltage, µV (300µV/100)/20mV [(60µV)(2)/100]/20mV 150 60
Input Offset Current, nA [(450pA)(350/2)Ω]/20mV [(450pA)(350Ω)/2]/20mV 4 4
CMR, dB 110dB→[(3.16ppm)(5V)]/20mV [(0.02% Match)(5V)]/20mV 790 500
Total Absolute Error 3944 5564
Drift to 85
°
C
Gain Drift, ppm/°C (50ppm + 10ppm)(60°C) (100ppm/°C Track)(60°C) 3600 6000
Input Offset Voltage Drift, µV/°C [(0.4µV/°C)(60°C)]/20mV [(1.6µV/°C)(60°C)]/20mV 1200 4800
Output Offset Voltage Drift, µV/°C[6µV/°C)(60°C)]/100/20mV [(1.1µV/°C)(2)(60°C)]/100/20mV 180 66
Total Drift Error 4980 10866
Resolution
Gain Nonlinearity, ppm of Full Scale 15ppm 10ppm 15 10
Typ 0.1Hz to 10Hz Voltage Noise, µV
P-P
0.28µV
P-P
/20mV (0.3µV
P-P
)(√2)/20mV 14 21
Total Resolution Error 29 31
Grand Total Error 8953 16461
G = 100, V
S
= ±15V
All errors are min/max and referred to input.
Table 1. “Roll Your Own” vs LT1167 Error Budget
ERROR, ppm OF FULL SCALE
Current Source
Figure 7 shows a simple, accurate, low power program-
mable current source. The differential voltage across Pins
2 and 3 is mirrored across R
G
. The voltage across R
G
is
amplified and applied across R
X
, defining the output
current. The 50µA bias current flowing from Pin 5 is
buffered by the LT1464 JFET operational amplifier. This
has the effect of improving the resolution of the current
source to 3pA, which is the maximum I
B
of the LT1464A.
Replacing R
G
with a programmable resistor greatly
increases the range of available output currents.
–
+
–
+
–
+
350Ω
350Ω
350Ω
350Ω
10V
10k**
PRECISION BRIDGE TRANSDUCER
LT1167 MONOLITHIC
INSTRUMENTATION AMPLIFIER
G = 100, R
G
= ±10ppm TC
SUPPLY CURRENT = 1.3mA MAX
“ROLL YOUR OWN” INST AMP, G = 100
* 0.02% RESISTOR MATCH, 3ppm/°C TRACKING
** DISCRETE 1% RESISTOR, ±100ppm/°C TC
100ppm TRACKING
SUPPLY CURRENT = 1.35mA FOR 3 AMPLIFIERS
1167 F06
R
G
499Ω
1/4
LT1114A
1/4
LT1114A
1/4
LT1114A
10k**
202Ω**
10k*
10k*
10k*
10k*
–
+
LT1167C
REF
APPLICATIO S I FOR ATIO
WUUU