THS4601 Datasheet, PDF (20/27 Pages) Texas Instruments – WIDEBAND, FET-INPUT OPERATIONAL AMPLIFIER

THS4601
SLOS388B – OCTOBER 2001 – REVISED JUNE 2002
APPLICATION INFORMATION
overdrive recovery (continued)
RISING EDGE OVERDRIVE RECOVERY
20
4
Gain = 5,
15 VIN = 5.57 VPP,
3
Recovery Time = 340 ns
10
Output 2
5
1
0
0
Input
–5
–1
–10
–2
–15
–3
–20
–4
0
1
2
3
4
Time – µs
Figure 36
RISING EDGE OVERDRIVE RECOVERY
20
4
Gain = 5,
15 VIN = 6 VPP,
3
Recovery Time = 680 ns
10
2
5
1
0
0
–5
–1
Input
–10
–2
Output
–15
–3
–20
–4
0
1
2
3
4
Time – µs
Figure 38
FALLING EDGE OVERDRIVE RECOVERY
20
4
15
3
Output
10
2
5
Input
1
0
0
–5
–1
–10
–2
Gain = 5,
–15 VIN = 5.57 VPP,
–3
Recovery Time = 320 ns
–20
–4
0
1
2
3
4
Time – µs
Figure 37
FALLING EDGE OVERDRIVE RECOVERY
20
4
15
3
Output
10
2
5
Input
1
0
0
–5
–1
–10
–2
Gain = 5,
–15 VIN = 6 VPP,
–3
Recovery Time = 540 ns
–20
–4
0
1
2
3
4
Time – µs
Figure 39
high frequency continuous wave amplification
When presented with high frequency sinusoids in low-gain configurations (G < 5), the THS4601 experiences
a relatively large differential input voltage between the two input terminals of the amplifier. As this differential
input voltage increases, the internal slew-boosting circuitry can cause some transistors in the signal path to
enter the cutoff region of operation. As the derivative of the signal changes signs, these transistors suffer from
a short recovery time period, generating appreciable levels of distortion. This behavior is depicted in the graph
Harmonic Distortion vs Frequency. At 2 MHz with a 2 V_PP output signal, the distortion rises significantly. For most
high-gain configurations including transimpedance applications, this phenomena is not problematic.
slew rate performance with varying input step amplitude and rise/fall time
Some FET input amplifiers exhibit the peculiar behavior of having a larger slew rate when presented with smaller
input voltage steps and slower edge rates due to a change in bias conditions in the input stage of the amplifier
under these circumstances. This phenomena is most commonly seen when FET input amplifiers are used as
voltage followers. As this behavior is typically undesirable, the THS4601 has been designed to avoid these
issues. Larger amplitudes lead to higher slew rates, as would be anticipated, and fast edges do not degrade
the slew rate of the device.
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