DATA SHEET
KH563
+VCC (+15)
SUMMARY DESIGN EQUATIONS AND DEFINITIONS
R – Feedback resistor
from output to inverting
input
R = G +1 R − A R
(
)
+
f
f
o
v
i
6.8m F
.1m F
Cx
10.5pF
23
4
19
8
V
i
(Pi)
R −R
f
o
+
Ro
R =
R – Gain setting
g
g
Vo
A −1
Rs
50W
v
KH563
resistor from inverting
input to ground
(Po)
18
RL
-
50W
5,10,15,
20
21
1
2
C – External
C =
x
x
R
Rf
410W
o
compensation capacitor
from output to
pin 19 (in pF)
− 0.08
Resistor Values
shown result in:
300 1−
Rg
40W
R
g
R
= 50W
o
.1m F
6.8m F
+
A
= +10
v
Where:
R – Desired equivalent output impedance
(no-load gain)
o
AL = +5 [14dB]
(gain to 50W load)
-VCC (-15)
A – Non-inverting input to output voltage
v
gain with no load
Figure 1:Test Circuit
G – Internal current gain from inverting input
to output = 10 1%
Design Equations
R – Internal inverting input impedance = 14Ω %5
i
R = G +1 R − A R
(
)
R – Non-inverting input termination resistor
f
o
v
i
s
R – Load resistor
L
Where:
R −R
A – Voltage gain from non-inverting input to
f
o
L
R =
g
G
≡ forward current gain
(=10)
load resistor
A −1
v
R
≡ inverting node input
resistance (=14Ω)
≡ desired output
impedance
≡ desired non-
inverting voltage
gain with no load
i
KH563 Description of Operation
R
Looking at the circuit of Figure 1 (the topology and
resistor values used in setting the data sheet specifica-
tions), the KH563 appears to bear a strong external
resemblance to a classical op amp. As shown in the
simplified block diagram of Figure 2, however, it differs in
several key areas. Principally, the error signal is a
current into the inverting input (current feedback) and the
forward gain from this current to the output is relatively
low, but very well controlled, current gain. The KH563
has been intentionally designed to have a low internal
gain and a current mode output in order that an equivalent
output impedance can be achieved without the series
matching resistor more commonly required of low output
impedance op amps. Many of the benefits of a high loop
gain have, however, been retained through a very careful
control of the KH563’s internal characteristics.
f
R +R 1+
R
A
f
i
o
R
g
R =
o
R
i
v
G +1+
R
g
R
i
G −
R
R
R
f
f
A = 1+
v
R
R
i
g
G +1+
g
Performance Equations
Simplified Circuit Description
Looking at the KH563’s simplified schematic in Figure 2,
the amplifier’s operation may be described. Going from
the non-inverting input at pin 8 to the inverting input at pin
18, transistors Q1 – Q4 act as an open loop unity gain
buffer forcing the inverting node voltage to follow the non-
inverting voltage input.
The feedback and gain setting resistors determine both
the output impedance and the gain. R predominately
f
sets the output impedance (R ), while R predominately
o
g
determines the no load gain (A ). solving for the required
v
Transistors Q3 and Q4 also act as a low impedance (14Ω
R and R , given a desired R and A , yields the design
f
g
o
v
looking into pin 18) path for the feedback error current.
equations shown below. Conversely, given an R and R ,
f
g
This current, (i ), flows through those transistors into a
err
the performance equations show that both R and R play
f
g
very well defined current mirror having a gain of 10 from
this error current to the output. The current mirror outputs
act as the amplifier output.
a part in setting R and A . Independent R and A
o
v
o
v
adjustment would be possible if the inverting input imped-
ance (R ) were 0 but, with R = 14Ω as shown in the
i
i
specification listing, independent gain and output imped-
The input stage bias currents are supply voltage inde-
pendent. Since these set the bias level for the whole
ance setting is not directly possible.
6
REV. 1A January 2008
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
