HA2556 Datasheet, PDF (14/20 Pages) Intersil Corporation – Wideband Four Quadrant Analog Multiplier (Voltage Output)

HA2556
DESIGN INFORMATION (Continued)
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.
Square Root
The Square Root function can serve as a precision/wide
bandwidth compander for audio or video applications. A
compander improves the Signal to Noise Ratio for your sys-
tem by amplifying low level signals while attenuating or com-
pressing large signals (refer to Figure 17; X^0.5 curve). This
provides for better low level signal immunity to noise during
transmission. On the receiving end the original signal may
be reconstructed with the standard Square function.
ACos(ω_Ατ) ^VX⁺
HA-2556
V_OUT
AUDIO
+
-
V_X -
X
A
W
1/5V
+
∑
CCos(ω_Cτ) VY+
CARRIER
+
-
Y
-
Z
V_Z +
+
-
V_Y -
V_Z -
W = ^A-₁---_0C-- ( Cos ( ω_C – ω_A) τ + Cos ( ω_C + ω_A) τ)
FIGURE 6. AM SIGNAL GENERATION
AM SIGNAL ^VX⁺
HA-2556
V_OUT
+
-
V_X -
X
A
W
+
1/5V
∑
CARRIER ^VY⁺
+
Y
-
-
Z
V_Z +
+
-
V_Y -
V_Z -
LIKE THE FREQUENCY DOUBLER YOU GET AUDIO CENTERED AT DC
AND 2F_C.
FIGURE 7. SYNCHRONOUS AM DETECTION
ACos(ωτ) ^VX⁺
HA-2556
V_OUT
+
-
V_X -
X
A
W
+
1/5V
∑
ACos(ωτ+φ) ^VY⁺
+
Y
-
-
Z
V_Z +
+
-
V_Y -
V_Z -
W = -^A1--₀-²- ( Cos ( φ) + Cos ( 2ωτ + φ) )
DC COMPONENT IS PROPORTIONAL TO Cos(f).
FIGURE 8. PHASE DETECTION
Communications
The Multiplier configuration has applications in AM Signal Gener-
ation, Synchronous AM Detection and Phase Detection to men-
tion a few. These circuit configurations are shown in Figure 6,
Figure 7 and Figure 8. The HA-2556 is particularly useful in
applications that require high speed signals on all inputs.
Each input X, Y and Z has similar wide bandwidth and input
characteristics. This is unlike earlier products where one
input was dedicated to a slow moving control function as is
required for Automatic Gain Control. The HA-2556 is versa-
tile enough for both.
Although the X and Y inputs have similar AC characteristics, they
are not the same. The designer should consider input parame-
ters such as small signal bandwidth, ac feedthrough and 0.1dB
gain flatness to get the most performance from the HA-2556.
The Y channel is the faster of the two inputs with a small signal
bandwidth of typically 57MHz verses 52MHz for the X channel.
Therefore in AM Signal Generation, the best performance will be
obtained with the Carrier applied to the Y channel and the modu-
lation signal (lower frequency) applied to the X channel.
Scale Factor Control
The HA-2556 is able to operate over a wide supply voltage range
±5V to ±17.5V. The ±5V range is particularly useful in video appli-
cations. At ±5V the input voltage range is reduced to ±1.4V. The
output cannot reach its full scale value with this restricted input,
so it may become necessary to modify the scale factor. Adjusting
the scale factor may also be useful when the input signal itself is
restricted to a small portion of the full scale level. Here we can
make use of the high gain output amplifier by adding external
gain resistors. Generating the maximum output possible for a
given input signal will improve the Signal to Noise Ratio and
Dynamic Range of the system. For example, let’s assume that
the input signals are 1V_PEAK each. Then the maximum output for
the HA-2556 will be 200mV. (1V x 1V / (5V) = 200mV. It would be
nice to have the output at the same full scale as our input, so let’s
add a gain of 5 as shown in Figure 9.
A
V_X +
+
-
V_X -
HA-2556
X
V_OUT
A
W
1/5V
+
∑
1kΩ
B
V_Y +
+
Y
-
Z
V_Z +
+
R_F
-
-
V_Y- _{ExternalGain = R-}^R_{---GF-- + 1} V_Z-
250Ω
R_G
FIGURE 9. EXTERNAL GAIN OF 5
One caveat is that the output bandwidth will also drop by this
factor of 5. The multiplier equation then becomes:
W = -⁵--^A-₅---^B- = A × B
Spec Number 511063-883
8-20