AD5539 데이터 시트보기 (PDF) - Analog Devices

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AD5539

Operational Amplifier Ultrahigh Frequency

Analog Devices 

Figures 21 and 22 show the small and large signal pulse re-

sponses of the general purpose inverter circuit of Figure 17, with

CLEAD = 1.5 pF, RLAG = 330 Ω and CLAG = 3.5 pF.

AD5539

Figure 21. Small Signal Pulse Response of the (Figure 17)

Inverter Circuit; Vertical Scale: 50 mV/div; Horizontal

Scale: 5 ns/div

Figure 23. A Gain of 2 Inverter Circuit with the CLEAD

Capacitor Connected to Pin 12

Figure 22. Large Signal Response of the (Figure 17)

Inverter Circuit; Vertical Scale: 200 mV/div, Horizontal

Scale: 5 ns/div

A CLEAD capacitor may be used to limit the circuit bandwidth

and to achieve a single pole response free of overshoot



 –3 dB

frequency

=

2π

1

R2 CLEAD





If this option is selected, it is recommended that a CLEAD be

connected between Pin 12 and the summing junction, as shown

in Figure 23. Pin 12 provides a separately buffered version of

the output signal. Connecting the lead capacitor here avoids the

excess output-stage phase shift and subsequent oscillation prob-

lems (at approx. 350 MHz) which would otherwise occur when

using the circuit of Figure 17 with a CLEAD of more than about

2 pF.

Figure 24 shows the response of the circuit of Figure 23 for each

connection of CLEAD. Lag components may also be added to this

circuit to further tailor its response, but, in this case, the results

will be slightly less satisfactory than connecting CLEAD directly

to the output, as was done in Figure 17.

Figure 24. Response of the Circuit of Figure 23 with

CLEAD = 10 pF

A General Purpose Voltage Follower Circuit

Noninverting (voltage follower) circuits pose an additional com-

plication, in that when a lag network is used, the source imped-

ance will affect the noise gain. In addition, the slightly greater

bandwidth of the noninverting configuration makes any excess

phase shift due to the output stage more of a problem.

For example, a gain of 3 noninverting circuit with CLEAD con-

nected normally (across the feedback resistor – Figure 25) will

require a source resistance of 200 Ω or greater to prevent UHF

oscillation; the extra source resistance provides some damping

as well as increasing the noise gain. The frequency response plot

of Figure 26 shows that the highest –3 dB frequency of all the

applications circuits can be achieved using this connection, un-

fortunately, at the expense of a noise gain of 14.2.

REV. B

–9–

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