The OPA657 device combines a high-gain bandwidth, low-distortion, voltage-feedback
operational amplifier with a low-voltage noise JFET-input stage to offer a very high dynamic range
amplifier for high-precision ADC (analog-to-digital converter) driving or wideband transimpedance
applications. Photodiode applications see improved noise and bandwidth using this decompensated,
high-gain bandwidth amplifier.
Very low level signals can be significantly amplified in a single OPA657 gain stage with
exceptional bandwidth and accuracy. Having a high 1.6-GHz gain bandwidth product gives greater than
10-MHz signal bandwidths up to gains of 160 V/V (44 dB). The very low input bias current and
capacitance supports this performance even for relatively high source impedances.
Broadband photodetector applications benefit from the low-voltage noise JFET inputs for
the OPA657. The JFET input contributes virtually no current noise while for broadband applications,
a low voltage noise is also required. The low 4.8 nV/√Hz input voltage noise
provides exceptional input sensitivity for higher bandwidth applications. The example shown below
gives a total equivalent input noise current of 1.8 pA/√Hz over a 10-MHz
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