ha1-2557/883 Intersil Corporation, ha1-2557/883 Datasheet - Page 11

• Manufacturer Part Number: ha1-2557/883
• Description: Wideband Four Quadrant Analog Multiplier Current Output
• Manufacturer: Intersil Corporation

DESIGN INFORMATION
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.
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
output I to V converter using R
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.
WHICH EVALUATES TO:
ACOS(
I
FIGURE 5. FREQUENCY DOUBLER
OUT
)
ACos
=
--------
20K
A
V
V
V
V
2
Y
X
Y
X
+
+
-
-
1/10KV
1
ACos
+
+
+
-
-
Cos 2
Z
which is trimmed to provide
X
Y
X
=
10kV
R
Z
(Continued)
I
OUT
I
OUT
HA2557
8-22
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/ s 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-
nal R
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.
-15V
V
Y
1N914
Z
5k
resistor, trimmed to provide an accurate 4V fullscale
1.0
FIGURE 6. AUTOMATIC GAIN CONTROL
I
0.01
OUT
NC
NC
NC
20k
+15V
1
2
3
4
5
6
7
8
10k
Y
REF
3pF
+
-
HA-2842
X
0.1 F
10k
2.5K
R
Spec Number
X
Z
0.01 F
+
-
16
15
14
13
12
11
10
HA-5127
9
0.1 F
0.01
NC
NC
NC
V
NC
X
1.0
511064-883
5.6V
V
+15V
OUT