Datasheet
AD734
Rev. E | Page 17 of 20
The possible two-tone intermodulation products are at 2 ×
9.95 MHz − 10.05 MHz ± 9.00 MHz and 2 × 10.05 − 9.95 MHz
± 9.00 MHz; of these, only the third-order products at 0.850 MHz
and 1.150 MHz are within the 10 MHz bandwidth of the AD734;
the desired output signals are at 0.950 MHz and 1.050 MHz.
Note that the difference between the desired outputs and third-
order products (see Figure 37) is approximately 78 dB, which
corresponds to a computed third-order intercept point of +46 dBm.
LOW DISTORTION MIXER
The AD734’s low noise and distortion make it especially suitable
for use as a mixer, modulator, or demodulator. Although the
AD734’s −3 dB bandwidth is typically 10 MHz and is established
by the output amplifier, the bandwidth of its X and Y interfaces
and the multiplier core are typically in excess of 40 MHz. Thus,
provided that the desired output signal is less than 10 MHz, as
is typically the case in demodulation, the AD734 can be used
with both its X and Y input signals as high as 40 MHz. One test
of mixer performance is to linearly combine two closely spaced,
equal-amplitude sinusoidal signals and then mix them with a
third signal to determine the mixer’s two-tone, third-order
intermodulation products.
CENTER 990 000.0Hz
RBW 1kHz
VBW 30Hz
SPAN 500 000.0Hz
ST 47.0sec
00827-020
REF – 10.0dB
m
10dB/DIV
RANGE – 5.0dBm
MARKER 950 000.0Hz
– 15.8dBm
AD734
X1
1
X2
2
U0
3
U1
4
U2
5
VP
14
DD
13
W
12
Z1
11
Z2
10
Y2
7
ER
9
VN
8
Y1
6
+15
V
OP177
–15V
0.1µF
0.1µF
00827-019
2kΩ
HP3326A
COMBINE
A + B
DATEL
DVC-8500
HP3326A
HIGH VOLTAGE
OPTION
HP3585A
WITH 10X PROBE
dBm REF TO 50Ω
Figure 37. AD734 Third-Order Intermodulation Performance for f
1
=
9.95 MHz, f
2
= 10.05 MHz, and f
0
= 9.00 MHz and for Signal Levels of f
1
= f
2
=
6 dBm and f
0
= +24 dBm (All Displayed Signal Levels Are Attenuated 20 dB by
the 10X Probe Used to Measure the Mixer’s Output)
Figure 36. AD734 Mixer Test Circuit
Figure 36 shows a test circuit for measuring the AD734’s
performance in this regard. In this test, two signals, at 10.05 MHz
and 9.95 MHz, are summed and applied to the AD734 X
interface. A second 9 MHz signal is applied to the AD734 Y
interface. The voltage at the U interface is set to 2 V to use the
full dynamic range of the AD734; that is, by connecting the W
and Z1 pins together, grounding the Y2 and X2 pins, and setting
U = 2 V, the overall transfer function is
V
YX
W
2
11
=
(14)
CENTER 990 000.0Hz
RBW 1kHz
VBW 10Hz
SPAN 500 000.0Hz
ST 156sec
00827-021
REF – 10.0dB
m
10dB/DIV
RANGE – 10.0dBm
MARKER 950 000.0Hz
– 21.8dBm
and W can be as high as 20 V p-p when X1 = 2 V p-p and Y1 =
10 V p-p. The 2 V p-p signal level corresponds to 10 dBm into a
50 Ω input termination resistor connected from X1 or Y1 to
ground.
If the two X1 inputs are at Frequency f
1
and Frequency f
2
and the
frequency at the Y1 input is f
0
, then the two-tone third-order
intermodulation products should appear at Frequency 2f
1
– f
2
±
f
0
and Frequency 2f
2
– f
1
± f
0
. Figure 37 and Figure 38 show the
output spectra of the AD734 with f
1
= 9.95 MHz, f
2
= 10.05 MHz,
and f
0
= 9.00 MHz for a signal level of f
1
= f
2
= 6 dBm and f
0
=
+24 dBm in Figure 37 and f
1
= f
2
= 0 dBm and f
0
= +24 dBm in
Figure 38. This performance is without external trimming of
the AD734 X and Y input offset voltages.
Figure 38. AD734 Third-Order Intermodulation Performance for f
1
=
9.95 MHz, f
2
= 10.05 MHz, and f
0
= 9.00 MHz and for Signal Levels of f
1
= f
2
=
0 dBm and f
0
= +24 dBm (All Displayed Signal Levels Are Attenuated 20 dB by
the 10X Probe Used to Measure the Mixer’s Output)