LMV792 datasheet(18/21 Pages) NSC

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Application Notes (Continued)

TABLE 1.

Transimpedance, A

3 dB Frequency

470000

50 pF

1.5 pF

350 kHz

470000

100 pF 2.0 pF

250 kHz

470000

200 pF 3.0 pF

150 kHz

47000

50 pF

4.5 pF

1.5 MHz

47000

100 pF 6.0 pF

1 MHz

47000

200 pF 9.0 pF

700 kHz

HIGH GAIN WIDEBAND TRANSIMPEDANCE

AMPLIFIER USING THE LMV792

The LMV792, dual, low noise, wide bandwidth, CMOS input

op amp IC can be used for compact, robust and integrated

solutions for sensing and amplifying wide-band signals ob-

tained from sensitive photodiodes. One of the two op amps

available can be used to obtain transimpedance gain while

the other can be used for amplifying the output voltage to

further enhance the transimpedance gain. The wide band-

width of the op amps (17 MHz) ensures that they are capable

of providing high gain for a wide range of frequencies. The

low input referred noise (5.8 nV/

) allows the amplifier to

deliver an output with a high SNR (signal to noise ratio). The

small MSOP-10 footprint saves space on printed circuit

boards and allows ease of design in portable products.

The circuit shown in Figure 13, has the first op amp acting as

a transimpedance amplifier with a gain of 47000, while the

second stage provides a voltage gain of 10. This provides a

total transimpedance gain of 470000 with a −3 dB bandwidth

of about 1.5 MHz, for a total input capacitance of 50 pF. The

frequency response for the circuit is shown in Figure 14

20116877

FIGURE 11. Frequency Response for A

TI = 470000

20116878

FIGURE 12. Frequency Response for A

TI = 47000

20116886

FIGURE 13. 1.5 MHz Transimpedance Amplifier, with

TI = 470000

20116879

FIGURE 14. 1.5 MHz Transimpedance Amplifier

Frequency Response

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