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V

HL,HH +

R1

ø R2 ø R3

R1

V

REF )

R1

ø R2 ø R3

R2

V

OUT

(3)

OPA698

R

2

402

Ω

R

1

200

Ω

R

3

200

Ω

V

REF

V

OUT

V

H

V

L

+2V

-2V

V

IN

S0044-01

Time (10ns/div)

4

3

2

1

0

-1

-2

-3

-4

V

IN

V

OUT

G052

Unity-Gain Buffer

OPA698M

SGLS287A – MAY 2005 – REVISED MARCH 2006

TYPICAL APPLICATIONS (continued)

The circuit operates as follow. When the input voltage is less than VHL then the output is limiting at VH. When the

input is greater than VHH then the output is limiting at VL, with VHL and VHH defined as the following:

Due to the inverting function realized by the Schmitt Trigger, VHL corresponds to VOUT = VH and VHH corresponds

to VOUT = VL.

Figure 61. High-Speed Schmitt Trigger

Figure 62 shows the Schmitt Trigger operating with VREF = +5 V. This gives us VHH = 2.4 V and VHL = 1.6 V. The

propagation delay for the OPA698 in a Schmitt Trigger configuration is 6 ns from high-to-low and 5 ns from

low-to-high.

Figure 62. Schmitt Trigger Time Domain Response for a 10-MHz Sinewave

Figure 63 shows a unity-gain voltage buffer using the OPA698. The feedback resistor (RF) isolates the output

from the input capacitance at the inverting input. RF = 24.9 Ω is recommended for unity-gain buffer applications.

RC is an optional compensation resistor that reduces the peaking typically seen at G = +1. Choosing RC = RS +

RF gives a unity-gain buffer with approximately the G = +2 frequency response. The frequency response for this

circuit is shown in the electrical characteristics curves.

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