HFA1106IP Просмотр технического описания (PDF) - Intersil

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HFA1106IP

315MHz, Low Power, Video Operational Amplifier with Compensation Pin

Intersil 

HFA1106

bandwidth significantly reduces system noise. Figure 3 illustrates

the noise performance of the HFA1106 with its bandwidth limited

to 40MHz by a 10pF CCOMP. As expected the noise decreases

by approximately 37% (100% x (1-√40MHz/100MHz)) compared

with Figure 2. The decrease is an even more dramatic 48%

versus the HFA1105 noise level in Figure 1.

enough, instability. To reduce this capacitance, the designer

should remove the ground plane under traces connected to

-IN, and keep connections to -IN as short as possible.

An example of a good high frequency layout is the Evaluation

Board shown in Figure 4.

Evaluation Board

The performance of the HFA1106 may be evaluated using

the HFA11XX Evaluation Board.

EN = 236µ VRMS

Figure 4 details the evaluation board layout and schematic.

Connecting RCOMP and CCOMP in series from socket pin 8

to the GND plane compensates the op amp. Cutting the

trace from pin 8 to the VH connector removes the stray par-

allel capacitance, which would otherwise affect the evalua-

tion. Additionally, the 500Ω feedback and gain setting

resistors should be changed to the proper value for the gain

being evaluated.

FIGURE 3. HFA1106 NOISE PERFORMANCE,

COMPENSATED, AV = +2, RF = 100Ω, CC = 10PF

Additionally, compensating the HFA1106 allows the use of a

lower value RF for a given gain. The decreased bandwidth

due to CCOMP keeps the amplifier stable by offsetting the

increased bandwidth from the lower RF . As noted previ-

ously, a lower value RF provides the double benefit of

reduced DC errors and lower total noise.

Less Lot-to-Lot Variability

External compensation provides another advantage by

allowing designers to set the op amp’s performance with a

precision external component. On-chip compensation

capacitors can vary by 10-20% over the process extremes.

A precise external capacitor dominates the on-chip compen-

sation for consistent lot-to-lot performance and more robust

designs. Compensating high frequency amplifiers to lower

bandwidths can simplify design tasks and ensure long term

manufacturability.

To order evaluation boards (part number HFA11XXEVAL),

please contact your local sales office.

VH

1

+IN

OUT

V+

VL V-

GND

TOP LAYOUT

PC Board Layout

This amplifier’s frequency response depends greatly on the

care taken in designing the PC board. The use of low

inductance components such as chip resistors and chip

capacitors is strongly recommended, while a solid

ground plane is a must!

Attention should be given to decoupling the power supplies.

A large value (10µF) tantalum in parallel with a small value

(0.1µF) chip capacitor works well in most cases.

Terminated microstrip signal lines are recommended at the

device’s input and output connections. Capacitance, para-

sitic or planned, connected to the output must be minimized,

compensated for by increasing CCOMP, or isolated by a

series output resistor.

Care must also be taken to minimize the capacitance to

ground at the amplifier’s inverting input (-IN), as this capaci-

tance causes gain peaking, pulse overshoot, and if large

BOTTOM LAYOUT

510

R1

1

50Ω

2

IN

3

4

10µF 0.1µF

-5V

510

8

7

6

5

GND

VH

0.1µF

50Ω

10µF

+5V

OUT

VL

GND

FIGURE 4. EVALUATION BOARD SCHEMATIC AND LAYOUT

3-33

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