The information contained in this section has been developed through characterization by Intersil Semiconductor and is for use as

application and design information only. No guarantee is implied.

8-22

HA2557

FIGURE 5. FREQUENCY DOUBLER

Although the X and Y inputs have similar AC characteristics,

they are not the same. The designer should consider input

parameters such as small signal bandwidth and ac

feedthrough to get the most performance from the HA-2557.

The Y channel is the faster of the two inputs with a small sig-

nal bandwidth of typically 130MHz verses 75MHz for the X

channel. Therefore in AM Signal Generation, the best perfor-

mance will be obtained with the Carrier applied to the Y

channel and the modulation signal (lower frequency) applied

to the X channel.

Operation Over a Wide Supply Range

The HA-2557 is able to operate over a wide supply voltage

range

±5V to ±17.5V. The ±5V range is particularly useful in

video applications. At

±5V the input voltage range is reduced

to

±1.4V limiting the fullscale output current. Another current

output option is the HA-2556 voltage output multiplier config-

ured for current output with an output sensing resistor (Refer

to the HA-2556 datasheet).

Automatic Gain Control

Figure 6 shows the HA-2557 configured in an Automatic

Gain Control or AGC application. The HA-2842 serves as an

an accurate 4V Fullscale conversion. Refer to Voltage

Output Conversion for more details about this function. The

HA-5127 low noise amplifier provides the gain control signal

to the X input. This control signal sets the peak output volt-

age of the multiplier to match the preset reference level. The

feedback network around the HA-5127 provides a response

time adjustment. High frequency changes in the peak are

rejected as noise or the desired signal to be transmitted.

These signals do not indicate a change in the average peak

value and therefore no gain adjustment is needed. Lower

frequency changes in the peak value are given a gain of -1

for feedback to the control input. At DC the circuit is an inte-

grator automatically compensating for offset and other con-

stant error terms.

1/10KV

Ω

X

Y

ACOS(

ωτ)

ACos

ωτ

()

×

()

10kV

Ω I

OUT

()

=

I

OUT

A

2

20K

ωτ

()

+

()

=

WHICH EVALUATES TO:

+

-

+

-

X

FIGURE 6. AUTOMATIC GAIN CONTROL

This multiplier has the advantage over other AGC circuits, in

that the signal bandwidth is not affected by the control signal

gain adjustment.

Voltage Output Conversion

The HA-2842 is an excellent choice to perform the output

current to voltage conversion as shown in Figure 7. The

combination of 400V/

µs slew rate and 80MHz Gain Band-

width product will maintain signal dynamics while providing a

full scale

±4V output. The HA-2842 also provides a hefty out-

put drive capability of 100mA.

This voltage feedback amplifier takes advantage of the inter-

conversion. The parasitic capacitance at the negative input

of the HA-2842 must be compensated with a 3pF capacitor

from pin 2 to pin 6. This compensation will also insure that

the amp will see a noise gain of 2 at its crossover frequency,

the minimum required for stability with this device. The full

power bandwidth curve and large signal pulse response for

this circuit are shown in Typical Performance Curves. The

fast slew rate of the HA-2842 results in a minimal reduction

of bandwidth for large signals.

5k

Ω

10k

Ω

HA-5127

0.01

µF

10k

Ω

0.1

µF

1N914

5.6V

0.1

µF

+15V

20k

Ω

14

15

16

9

13

12

11

10

1

2

3

4

5

7

6

8

+15V

NC

NC

NC

-15V

NC

REF

NC

NC

NC

X

0.01

µ

1.0

µ

3pF

1.0

µ

0.01

µ

2.5K

+

-

HA-2842

+

-

Y

X

Spec Number

511064-883