OPA134 Datasheet, PDF (14/22 Pages) Burr-Brown (TI) – High Performance AUDIO OPERATIONAL AMPLIFIERS TM

OPA134, OPA2134, OPA4134
SBOS058A – DECEMBER 1997 – REVISED OCTOBER 2015
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Feature Description (continued)
7.3.5 Output Current Limit
Output current is limited by internal circuitry to approximately ±40 mA at 25°C. The limit current decreases with
increasing temperature, as shown in Figure 19.
7.4 Device Functional Modes
7.4.1 Noise Performance
Circuit noise is determined by the thermal noise of external resistors and operational amplifier noise. Operational
amplifier noise is described by two parameters: noise voltage and noise current. The total noise is quantified by
the equation:
V_n(total) = (i_nR_S )² e_n2 + 4kTR_S
(1)
With low source impedance, the current noise term is insignificant and voltage noise dominates the noise
performance. At high source impedance, the current noise term becomes the dominant contributor.
Low-noise bipolar operational amplifiers such as the OPA27 and OPA37 provide low voltage noise at the
expense of a higher current noise. However, OPA134 series operational amplifiers provide both low voltage
noise and low current noise. This provides optimum noise performance over a wide range of sources, including
reactive source impedances; refer to Figure 6. Above 2-kΩ source resistance, the operational amplifier
contributes little additional noise; the voltage and current terms in the total noise equation become insignificant
and the source resistance term dominates. Below 2 kΩ, operational amplifier voltage noise dominates over the
resistor noise, but compares favorably with other audio operational amplifiers such as the OP176.
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