Quadrature Modulator
CMX993/CMX993W
Delta
4
[T1]
-48.78 dB
-36.07214429 kHz
RBW
VBW
SWT
1
1
kHz
kHz
RF Att
Mixer
Unit
20 dB
-20 dBm
dBm
Delta
2
[T1]
-50.78 dB
RBW
VBW
SWT
1
1
kHz
kHz
RF Att
Mixer
Unit
20 dB
-20 dBm
dBm
Ref Lvl
dBm
Ref Lvl
dBm
5
200 ms
5
29.97995992 kHz
200 ms
5
0
5
0
1
1
4
1
2
3
[T1]
-3.10 dBm
1
2
2
1
[T1]
0.00 dBm
B
LN
B
LN
1
30.00921844 MHz
-48.78 dB
49.99270541 MHz
-50.78 dB
[T1]
[T1]
[T1]
[T1]
[T1]
[T1]
[T1]
-10
-20
-30
-40
-50
-60
-70
-80
-36.07214429 kHz
-39.72 dB
-10
-20
-30
-40
-50
-60
-70
-80
29.97995992 kHz
-26.28 dBm
-28.05611222 kHz
-40.09 dB
50.00024048 MHz
-46.42 dB
2
14.10821643 kHz
-63.92 dB
15.07014028 kHz
1SA
EXT
1SA
EXT
28.05611222 kHz
1
2
1
4
2
3
-90
-95
-90
-95
Center 30 MHz
8
kHz/
Span 80 kHz
Center 50 MHz
8
kHz/
Span 80 kHz
Two-tone signal at 30MHz, +3dBm PEP output,
modulator driven from ‘filter amp’,
LO = 60MHz, -10dBm.
0dBm single-tone at 50MHz, modulator driven from
‘Input amp’, LO = 100MHz, -10dBm.
7.2
Intermodulation and Modulator Spurious
When selecting an I/Q modulator for a particular application users should take care as intermodulation
performance figures given in datasheets can sometimes be difficult to interpret. Some devices similar to
the CMX993 quote ‘output IP3’ performance that is only achieved at reduced input / output levels. It has
been observed that at their rated output power the performance of these devices is degraded (see Figure
6). By contrast the CMX993 output IP3 is constant when measured with different input / output levels for a
given frequency. Typical ‘Equivalent Output IP3’ is in the range 23dBm to 25dBm at 400MHz; lower values
can be expected at higher frequencies and below 100MHz.
0dBm PEP (rated output power)
26
25
24
23
22
CMX993
Competitor I/Q Modulator
21
20
19
18
17
16
-15
-13
-11
-9
-7
-5
-3
-1
Output level per tone / dBm
Figure 6 – Variation in Effective Equivalent IP3 with signal level
Another issue that has been observed with alternative I/Q modulator devices is that the third-order
products are not always the largest distortion products. This will be observed in Figure 7 where a
competitor’s device exhibits larger distortion products resulting from the third harmonics of the modulation
than the classic 3rd order intermodulation products. Figure 8 shows the equivalent CMX993 performance
at the same output power and frequency.
2013 CML Microsystems Plc
18
D/993/10
CMLMICRO [ CML MICROCIRCUITS ]
