LMH6624MF Datasheet, PDF (15/31 Pages) Texas Instruments – LMH6624/LMH6626 Single/Dual Ultra Low Noise Wideband Operational Amplifier

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LMH6624
SNOSA42F – NOVEMBER 2002 – REVISED MARCH 2013
APPLICATION SECTION
Figure 50. Non-Inverting Amplifier Configuration
INTRODUCTION
The LMH6624/LMH6626 are very wide gain bandwidth, ultra low noise voltage feedback operational amplifiers.
Their excellent performances enable applications such as medical diagnostic ultrasound, magnetic tape & disk
storage and fiber-optics to achieve maximum high frequency signal-to-noise ratios. The set of characteristic plots
in the "Typical Performance" section illustrates many of the performance trade offs. The following discussion will
enable the proper selection of external components to achieve optimum system performance.
BIAS CURRENT CANCELLATION
To cancel the bias current errors of the non-inverting configuration, the parallel combination of the gain setting
(R_g) and feedback (R_f) resistors should equal the equivalent source resistance (R_seq) as defined in Figure 50.
Combining this constraint with the non-inverting gain equation also seen in Figure 50, allows both R_f and R_g to
be determined explicitly from the following equations:
R_f = A_VR_seq and R_g = R_f/(A_V-1)
(1)
When driven from a 0Ω source, such as the output of an op amp, the non-inverting input of the
LMH6624/LMH6626 should be isolated with at least a 25Ω series resistor.
As seen in Figure 51, bias current cancellation is accomplished for the inverting configuration by placing a
resistor (R_b) on the non-inverting input equal in value to the resistance seen by the inverting input (R_f||(R_g+R_s)).
R_b should to be no less than 25Ω for optimum LMH6624/LMH6626 performance. A shunt capacitor can minimize
the additional noise of R_b.
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