DATA SHEET

KH560

8

REV. 1A January 2004

Figure 4: Voltage Gain Derivation

considerably. Also, if G were very large the voltage gain

expression would reduce to the familiar non-inverting op

amp gain equation. These two performance equations,

shown below, provide a means to derive the design

output impedance.

Performance Equations

Design Equations

Equivalent Model

Given that the physical feedback and gain setting

resistors have been determined in accordance with the

design equations shown above, an equivalent model

may be created for the gain to the load where the

amplifier block is taken as a standard op amp. Figure 5

shows this analysis model and the resulting gain

equation to the load.

Figure 5: Equivalent Model

This model is used to generate the DC error and noise

performance equations. As with any equivalent model,

the primary intent is to match the external terminal

characteristics recognizing that the model distorts the

internal currents and voltages. In this case, the model

would incorrectly predict the output pin voltage swing for

a given swing at the load. But it does provide a simplified

means of getting to the external terminal characteristics.

As shown in the test circuit of Figure 1, the KH560 requires

an external compensation capacitor from the output to

pin 19. The recommended values described here assume

that a maximally flat frequency response into a matched

load is desired.

the desired value of output impedance and to a lesser

degree on the desired gain.

Note from Figure 2, the

simplified internal schematic, that the actual total

the internal 10pF from pin 19 to the compensation nodes.

shown below.

recognize that [taking V positive]

VV

Gi

R

solving for V from two directions

V

V

iR

G 1 iR

solving for i

from this

i

V

G1 R

R

then

VV

VR

G1 R

R

and, substituting for V and i

in the original V expression

VV 1

GR

R

i

o

err

f

i

err

i

err

g

err

err

i

gi

i

ii

gi

err

o

oi

f

=+

=−

=

+

()

=

+

()

+

=−

+

()

+

=+

−

−

−

−

−

−

ii

gi

f

g

v

o

i

f

g

i

f

i

g

v

f

g

i

G1 R

R

pulling an

R

R

out of the fraction

A

V

V

1

R

R

G

R

R

G1

R

R

note that A

1

R

R

G

G1

R0

+

()

+

















≡= +

−

++

























=+

+









=

R

RR

R

R

G

R

R

A

R

R

G

R

R

G

R

R

o

f

i

f

g

i

g

v

f

g

i

f

i

g

=

++













++

=+

−

++

























1

1

1

1

RG

R

A R

R

RR

A

f

ov

i

g

f

o

v

=+

()

−

=

−

−

1

1

Classical

op-amp

+

-

V

V

1

RR

R

R

RR

substituting in for R and R with their design

equation yields

V

V

A

R

RR

A (gain to load)

o

i

f

o

g

L

Lo

f

g

o

i

v

L

Lo

L

=+

−













+

=

+

=

C

300

R

1

2.0

R

pF intermediate equation

C

C

1

0.02 C

pF total compensation

1

og

t

1

1

=−













=

+

()