AD8067

Rev. 0 | Page 22 of 24

M 50ns CH1 288mV

T

Reference network:

3

2

2

1

3

C

R

||

R

Bandwidth

dB

π

=

−

+

Resistors R4 and R1 set the gain, in this case an inverting gain of 10

was selected. In this application, the input and output bandwidths

were set for approximately 10 Hz. The reference network was set for

a tenth of the input and output bandwidth, at approximately 1 Hz.

AD8067

C4

0.1

µF

C3

10

µF

+5V

R4

2.7k

Ω

R1

300

Ω

R3

30k

Ω

R2

70k

Ω

1k

Ω

C5

15

µF V

OUT

1

2

3

4

5

C1

47

µF

C2

6.8

µF

+5V

Figure 55. Gain of 2 Pulse Response

Single-Supply Operation

The AD8067 is well suited for low voltage single-supply

applications, given its N-channel JFET input stage and rail-to-rail

output stage. It is fully specified for 5 V supplies. Successful single-

supply applications require attention to keep signal voltages within

the input and output headroom limits of the amplifier. The input

stage headroom extends to 1.7 V (minimum) on a 5 V supply. The

center of the input range is 0.85 V. The output saturation limit

defines the hard limit of the output headroom. This limit depends

on the amount of current the amplifier is sourcing or sinking, as

shown in Figure 29.

Figure 56. Single-Supply Operation Schematic

High Gain, High Bandwidth Composite

Amplifier

Traditionally, an offset voltage is introduced in the input network

replacing ground as a reference. This allows the output to swing

about a dc reference point, typically midsupply. Attention to the

required headroom of the amplifier is important, in this case the

required headroom from the positive supply is 3 V; therefore 1.5 V

was selected as a reference, which allows for a 100 mV signal at the

input. Figure 56 shows the AD8067 configured for 5 V supply

operation with a reference voltage of 1.5 V. Capacitors C1 and C5

ac-couple the signal into an out of the amplifier and partially

determine the bandwidth of the input and output structures.

The composite amplifier takes advantage of combining key

parameters that may otherwise be mutually exclusive of a

conventional single amplifier. For example, most precision

amplifiers have good dc characteristics but lack high speed ac

characteristics. Composite amplifiers combine the best of both

amplifiers to achieve superior performance over their single op

amp counterparts. The AD8067 and the AD8009 are well suited for

a composite amplifier circuit, combining dc precision with high

gain and bandwidth. The circuit runs off a ±5 V power supply at

approximately 20 mA of bias current. With a gain of approximately

40 dB, the composite amplifier offers <1 pA input current, a gain

bandwidth product of 6.1 GHz, and a slew rate of 630 V/µsec.

1

1

2

1

3

C

R

Bandwidth

dB

–

π

=

5

2

1

3

C

R

Bandwidth

dB

–

V

L

OUTPUT

π

=

Resistors R2 and R3 set a 1.5 V output bias point for the output

signal to swing about. It is critical to have adequate bypassing to

provide a good ac ground for the reference voltage. Generally the

bandwidth of the reference network (R2, R3, and C2) is selected to

be one tenth that of the input bandwidth. This ensures that any

frequencies below the input bandwidth do not pass through the

reference network into the amplifier.