10k

100k

1M

10M

FREQUENCY (Hz)

-40

-30

-20

-10

0

10

20

10k

100k

1M

10M

100M

FREQUENCY (Hz)

-25

-20

-15

-10

-5

0

5

10

15

LMP7715, LMP7716, LMP7716Q

SNOSAV0E – MARCH 2006 – REVISED MARCH 2013

www.ti.com

Figure 52. Closed Loop Frequency Response

form yet another pole in the system and will prevent pairs of poles, or complex conjugates from forming. It is the

presence of pairs of poles that cause the peaking of gain. Figure 53 shows the frequency response of the

significantly reduces or eliminates the peaking.

Figure 53. Closed Loop Frequency Response

TRANSIMPEDANCE AMPLIFIER

In many applications the signal of interest is a very small amount of current that needs to be detected. Current

that is transmitted through a photodiode is a good example. Barcode scanners, light meters, fiber optic receivers,

and industrial sensors are some typical applications utilizing photodiodes for current detection. This current

needs to be amplified before it can be further processed. This amplification is performed using a current-to-

voltage converter configuration or transimpedance amplifier. The signal of interest is fed to the inverting input of

an op amp with a feedback resistor in the current path. The voltage at the output of this amplifier will be equal to

the negative of the input current times the value of the feedback resistor. Figure 54 shows a transimpedance

capacitance of the amplifier. The presence of all of these capacitances at higher frequencies might lead to less

stable topologies at higher frequencies. Care must be taken when designing a transimpedance amplifier to

prevent the circuit from oscillating.

With a wide gain bandwidth product, low input bias current and low input voltage and current noise, the

LMP7715/LMP7716/LMP7716Q are ideal for wideband transimpedance applications.

16

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