ISL28134_14 Datasheet, PDF (14/25 Pages) Intersil Corporation – 5V Ultra Low Noise, Zero Drift Rail-to-Rail Precis Op Amp

ISL28134
Typical Performance Curves T_A = +25°C, V_CM = 0V Unless otherwise specified. (Continued)
60
55
55
50
- OS
50
45
- OS
45
40
35
30
25
20
15
10
10
+OS
V_S = ±2.5V
A_V = 1V
R_L = 100k
V_OUT = 100mV_p-p
100
LOAD CAPACITANCE (pF)
1000
40
35
30
25
20
15
10
10
+OS
V_S = ±1.25V
A_V = 1V
R_L = 100k
V_OUT = 100mV_p-p
100
LOAD CAPACITANCE (pF)
1000
FIGURE 42. SMALL SIGNAL OVERSHOOT vs LOAD CAPACITANCE,
VS = ±2.5V
FIGURE 43. SMALL SIGNAL OVERSHOOT vs LOAD CAPACITANCE,
V_S = ±1.25V
Applications Information
Functional Description
The ISL28134 is a single 5V rail-to-rail input/output amplifier
that operates on a single or dual supply. The ISL28134 uses a
proprietary chopper-stabilized technique that combines a 3.5MHz
main amplifier with a very high open loop gain (174dB) chopper
amplifier to achieve very low offset voltage and drift (0.2µV,
0.5nV/°C) while having a low supply current (675µA). The very low
1/f noise corner <0.1Hz and low input noise voltage (8nV/√Hz at
100Hz) of the amplifier makes it ideal for low frequency precision
applications requiring very high gain and low noise.
This multi-path amplifier architecture contains a time continuous
main amplifier whose input DC offset is corrected by a
parallel-connected, high gain chopper stabilized DC correction
amplifier operating at 100kHz. From DC to ~10kHz, both
amplifiers are active with the DC offset correction active with
most of the low frequency gain provided by the chopper
amplifier. A 10kHz crossover filter cuts off the low frequency
chopper amplifier path leaving the main amplifier active out to
the -3dB frequency (3.5MHz GBWP).
The key benefits of this architecture for precision applications are
rail-to-rail inputs/outputs, high open loop gain, low DC offset and
temperature drift, low 1/f noise corner and low input noise
voltage. The noise is virtually flat across the frequency range
from a few MHz out to 100kHz, except for the narrow noise peak
at the amplifier crossover frequency (10kHz).
Power Supply Considerations
The ISL28134 features a wide supply voltage operating range. The
ISL28134 operates on single (+2.25V to +6.0V) or dual (±1.125 to
±3.0V) supplies. Power supply voltages greater than the +6.5V
absolute maximum (specified in the “Absolute Maximum Ratings”
on page 4) can permanently damage the device. Performance of
the device is optimized for supply voltages greater than 2.5V. This
makes the ISL28134 ideal for portable 3V battery applications that
require the precision performance. It is highly recommended that a
0.01µF or larger high frequency decoupling capacitor is placed
across the power supply pins of the IC to maintain high performance
of the amplifier.
Rail-to-rail Input and Output (RRIO)
Unlike some amplifiers whose inputs may not be taken to the power
supply rails or whose outputs may not drive to the supply rails, the
ISL28134 features rail-to-rail inputs and outputs. This allows the
amplifier inputs to have a wide common mode range (100mV
beyond supply rails) while maintaining high CMRR (135dB) and
maximizes the signal to noise ratio of the amplifier by having the
V_OH and V_OL levels be at the V+ and V- rails, respectively.
Low Input Voltage Noise Performance
In precision applications, the input noise of the front end
amplifier is a critical parameter. Combined with a high DC gain to
amplify the small input signal, the input noise voltage will result
in an output error in the amplifier. A 1µV_P-P input noise voltage
with an amplifier gain of 10,000V/V will result in an output offset
in the range of 10mV, which can be an unacceptable error
source. With only 250nV_P-P at the input, along with a flat noise
response down to 0.1Hz, the ISL28134 can amplify small input
signals with minimal output error.
The ISL28134 has the lowest input noise voltage compared to
other competitor Zero Drift amplifiers with similar supply
currents (see Table 1). The overall input referred voltage noise of
an amplifier can be expressed as a sum of the input noise
voltage, input noise current of the amplifier and the Johnson
noise of the gain-setting resistors used. The product of the input
noise current and external feedback resistors along with the
Johnson noise, increases the total output voltage noise as the
value of the resistance goes up. For optimizing noise
performance, choose lower value feedback resistors to minimize
the effect of input noise current. Although the ISL28134 features
a very low 200fA/Hz input noise current, at source impedances
>100kΩ, the input referred noise voltage will be dominated by
the input current noise. Keep source input impedances under
10kΩ for optimum performance.
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FN6957.6
October 14, 2014