AD8293G160 Analog Devices, AD8293G160 Datasheet - Page 10

• Manufacturer Part Number: AD8293G160
• Description: Low Cost, Zero-Drift In-Amp with Filter and Fixed Gain = 160
• Manufacturer: Analog Devices

Specifications of AD8293G160

• Filter Option: Yes
• Common Mode Input (v)min: +1.8V
• Common Mode Input (v)max: +5.5V
• Bandwidth G=10 (khz Typ): 0.5kHz
• Cmrr (db): 140dB
• Vcc-vee: 1.8V to 5.5V

AD8293G80/AD8293G160
THEORY OF OPERATION
The AD8293G80/AD8293G160 are precision current-mode
correction instrumentation amplifiers capable of single-supply
operation. The current-mode correction topology results in
excellent accuracy. Figure 18 shows a simplified diagram
illustrating the basic operation of the AD8293G80/AD8293G160
(without correction). The circuit consists of a voltage-to-current
amplifier (M1 to M6), followed by a current-to-voltage amplifier
(R2 and A1). Application of a differential input voltage forces a
current through External Resistor R1, resulting in conversion of
the input voltage to a signal current. Transistor M3 to Transistor
M6 transfer twice this signal current to the inverting input of
the op amp A1. Amplifier A1 and External Resistor R2 form
a current-to-voltage converter to produce a rail-to-rail output
voltage at V
Op amp A1 is a high precision auto-zero amplifier. This amplifier
preserves the performance of the autocorrecting, current-mode
amplifier topology while offering the user a true voltage-in,
voltage-out instrumentation amplifier. Offset errors are corrected
internally.
An external reference voltage is applied to the noninverting
input of A1 to set the output reference level. External Capacitor
C2 is used to filter out correction noise.
OUT
.
V
INP
EXTERNAL
2I
I
M1
I
R1
=
(V
V
CC
R1
INP
R1
– V
INN
)
2I
M2
I
V
INN
M5
Figure 18. Simplified Schematic
M3
I – I
Rev. 0 | Page 10 of 16
R1
M4
M6
I – I
I + I
V
BIAS
R1
R1
HIGH PSR AND CMR
Common-mode rejection and power supply rejection indicate
the amount that the offset voltage of an amplifier changes when
its common-mode input voltage or power supply voltage changes.
The autocorrection architecture of the AD8293G80/AD8293G160
continuously corrects for offset errors, including those induced
by changes in input or supply voltage, resulting in exceptional
rejection performance. The continuous autocorrection provides
great CMR and PSR performances over the entire operating
temperature range (−40°C to +85°C).
The parasitic resistance in series with R2 does not degrade CMR,
but causes a small gain error and a very small offset error.
Therefore, an external buffer amplifier is not required to drive
V
system costs over conventional instrumentation amplifiers.
1/f NOISE CORRECTION
Flicker noise, also known as 1/f noise, is noise inherent in the
physics of semiconductor devices and decreases 10 dB per decade.
The 1/f corner frequency of an amplifier is the frequency at which
the flicker noise is equal to the broadband noise of the amplifier. At
lower frequencies, flicker noise dominates, causing large errors
in low frequency or dc applications.
Flicker noise is seen effectively as a slowly varying offset
error, which is reduced by the autocorrection topology of the
AD8293G80/AD8293G160. This allows the AD8293G80/
AD8293G160 to have lower noise near dc than standard low
noise instrumentation amplifiers.
2I
REF
R1
V
REF
to maintain excellent CMR performance. This helps reduce
C2
R2
A1
V
R3
OUT
= V
C3
REF
+
2R2
R1
V
INP
– V
INN