lt5578 MOSA electronics corp., lt5578 Datasheet - Page 13

• Manufacturer Part Number: lt5578
• Description: 0.4ghz To 2.7ghz High Linearity Upconverting Mixer
• Manufacturer: MOSA electronics corp.

TYPICAL APPLICATIONS
The following examples illustrate the implementation and
performance of the LT5578 in some selected applications.
These circuits were evaluated using the board layout
shown in Figure 12.
450MHz Application
In this case, the LT5578 was evaluated for an application
with an IF input at 70MHz, an RF output of 450MHz and
a high side LO. The LO port is tuned for high side LO in-
jection at 520MHz. The matching networks for the three
ports are shown in Figure 8.
At the IF input, the 560pF capacitors are used mainly as
DC blocks, but also help tune out the parasitic inductance
of the transformer. The 82pF differential capacitor and
3.3nH chip inductors provide an impedance transforma-
tion between the IF input pins and the transformer. The
relatively low input frequency requires the use of chip
inductors instead of the short transmission lines that are
shown in Figure 2. The measured IF port return loss is
included in Figure 3.
The RF port impedance match is realized with a shunt 12pF
capacitor and a series 18nH inductor. The return loss with
this confi guration is better than 12dB from about 430MHz
to 505MHz and is plotted in Figure 7.
To tune the LO port, a series 6.8pF and shunt 4.7pF ca-
pacitor are used as shown. This combination provides a
10dB, or better, return loss from 435MHz to 580MHz as
shown in Figure 5. The series capacitor also provides DC
decoupling for the internal transformer at the LO input.
Figure 8. Schematic for 450MHz RF Application with 70MHz IF and 520MHz LO
70MHz
IF
TC4-1W+
4:1
560pF
560pF
82pF
3.3nH
3.3nH
13.7Ω
13.7Ω
Figure 9 shows measured conversion gain, noise fi gure
and OIP3 as a function of RF output frequency. At 450MHz,
the gain is –2.1dB with a NF of 9.3dB and an OIP3 of
23.8dBm.
2600MHz Application
For this application, the impedance match of the RF port is
optimized at 2600MHz and has a good return loss over the
range of 2200MHz to 2900MHz. The component values are
listed in Table 5 and typical output return loss is shown in
Figure 7. The IF input is matched at 240MHz as described
in Table 2. The LO port requires no external matching for
this band as its return loss is good for frequencies above
1.5GHz.
100nH
100nH
Figure 9. Gain, Noise Figure and OIP3 vs RF Frequency
in the 450MHz Application
4.7pF
6.8pF
12
10
–2
–4
8
6
4
2
0
420
LO
520MHz
12pF
18nH
RF OUTPUT FREQUENCY (MHz)
440
SSB NF
OIP3
GAIN
450MHz
RF
460
5578 F08
T
f
P
IF
A
IF
= 70MHz
= 25°C
= –5dBm/TONE
480
5578 F09
500
LT5578
32
30
28
26
24
22
20
18
16
13
5578f