LMH6624MA datasheet(16/20 Pages) NSC

16 / 20 page

Application Section (Continued)

SINGLE SUPPLY OPERATION

The LMH6624/LMH6626 can be operated with single power

supply as shown in Figure 8. Both the input and output are

capacitively coupled to set the DC operating point.

LOW NOISE TRANSIMPEDANCE AMPLIFIER

Figure 9 implements a low-noise transimpedance amplifier

commonly used with photo-diodes. The transimpedance

gain is set by R

f. Equation 4 provides the total input current

noise density (i

ni) equation for the basic transimpedance

configuration and is plotted against feedback resistance (R

showing all contributing noise sources in Figure 10. This plot

indicates the expected total equivalent input current noise

density (i

ni) for a given feedback resistance (Rf). The total

equivalent output voltage noise density (e

no)isini*Rf.

(5)

LOW NOISE INTEGRATOR

The LMH6624/LMH6626 implement a deBoo integrator

shown in Figure 11. Positive feedback maintains integration

linearity. The LMH6624/LMH6626’s low input offset voltage

and matched inputs allow bias current cancellation and pro-

vide for very precise integration. Keeping R

G and RS low

helps maintain dynamic stability.

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FIGURE 7. External Lag Compensation

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FIGURE 8. Single Supply Operation

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FIGURE 9. Transimpedance Amplifier Configuration

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FIGURE 10. Current Noise Density vs. Feedback

Resistance

LMH6624MA Datasheet(PDF) 16 Page - National Semiconductor (TI)