KH300 datasheet(5/7 Pages) CADEKA

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KH300

DATA SHEET

REV. 1A January 2004

Layout Considerations

To assure optimum performance the user should follow

good layout practices which minimize the unwanted

coupling of signals between nodes. During initial bread-

boarding of the circuit, use direct point to point wiring,

keeping lead lengths to less than 0.25”. The use of

solid, unbroken ground plane is helpful. Avoid wire-wrap

type pc boards and methods. Sockets with small, short

pin receptacles may be used with minimal performance

degradation although their use is not recommended.

Figure 1: Recommended Non-inverting Gain Circuit

Figure 2: Recommended Inverting Gain Circuit

During pc board layout keep all traces short and direct.

Rf and Rg should be as close as possible to pin 8 to

minimize capacitance at that point. For the same reason,

remove ground plane from the vicinity of pins 8 and 6.

In other areas, use as much ground plane as possible

on one side of the pc board. It is especially important to

provide a ground return path for current from the load

resistor to the power supply bypass capacitors. Ceramic

capacitors of 0.01 to 0.1

µF should be close to pins 13

and 16. Larger tantalum capacitors should also be

placed within one inch of these pins. To prevent signal

distortion caused by reflections from impedance mis-

matches, use terminated microstrip or coaxial cable

when the signal must traverse more than a few inches.

Since the pc board forms such an important part of the

circuit, much time can be saved if prototype boards of

any high frequency sections are built and tested early in

the design phase.

Controlling Bandwidth and Passband Response

As with any op amp, the ratio of the two feedback resistors

Rf and Rg, determines the gain of the KH300. Unlike

conventional op amps, however, the closed loop pole-

zero response of the KH300 is affected very little by the

value of Rg. Rg scales the magnitude of the gain, but

does not change the value of the feedback. Rf does

influence the feedback and so the KH300 has been

internally compensated for optimum performance with

Rf = 1500Ω, but any value of Rf > 500Ω may be used

with a single capacitor placed between pins 8 and 12

for compensation. See table 1. As Rf decreases, Cc

must increase to maintain flat gain. Large values of Rf

and Cc can be used together or separately to reduce

the bandwidth. This may be desirable for reducing the

noise bandwidth in applications not requiring the full fre-

quency response available.

Table 1: Bandwidth vs. Rf and Cc (Av = +20)

f±0.3dB

f-3.0dB

Ω)

(pF)

(MHz)

10.0

5.0

2.0

1.5

1.0

0.3

115

0.75

1.1

130

0.50

1.9

110

135

Low Gain Operation

The small amount of stray capacitance present at the

inverting input can cause peaking which increases with

decreasing gain. The gain setting resistor Rg is effectively

in parallel with this capacitance and so a frequency

domain pole results. With small Rg (Gain > 8), this pole

is at a high frequency and it affects the closed loop gain

of the KH300 only slightly. At lower values of gain, this

pole becomes significant. For example, at a gain of +2,

the gain may peak as much as 3dB at 75MHz, and

have a bandwidth exceeding 150MHz. The same

behavior does not exist for low inverting gains, however,

since the inverting input is a virtual ground which main-

tains a constant voltage across the stray capacitance.

Even at inverting gains << 1, the frequency response

remains unchanged.

0.01

µF

-15

KH300

Ω

Vin

Ω

1/2 Vo

+15

µF

0.01

µF

Ω

Av = 1 +

Rf = 1500Ω (internal)

0.01

µF

-15

KH300

Ω

Vin

Ω

1/2 Vo

+15

µF

0.01

µF

Ω

-Av =

Rf = 1500Ω (internal)

For Zin = 50Ω Select:

Rg||Ri = 50

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