QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1233A-X
1.5GHZ TO 3.8GHZ HIGH LINEARITY UPCONVERTING MIXER
2
APPLICATION NOTE
ABSOLUTE MAXIMUM RATINGS
Supply Voltage......................................................3.6V
LO Input Power.............................................. +10dBm
LO Input DC Voltage .................... -0.3V to V
CC
+ 0.3V
RF Output DC Current........................................ 60mA
IF Input Power (Differential).......................... +13dBm
IF
+
, IF
-
DC Currents ........................................... 60mA
T
JMAX
.................................................................150°C
Operating Temperature Range.............. -40°C to 85°C
Storage Temperature Range............... -65°C to 150°C
IF INPUT INTERFACE
The standard demonstration circuit 1233A-x can be re-
configured for other IF input frequencies. The details of
the matching circuit are omitted in this guide, since the
LT5579 datasheet presents in depth explanations and
the IC’s IF input differential impedance. Matching com-
ponent values for several common IF input frequencies
are listed in Table 2. Refer to the demonstration circuit
schematic in Figure 3.
Table 2. IF Input Component Values
IF Freq.
(MHz)
C1,C2
(pF)
C9 (1)
(pF)
C3
(pF)
TL1,TL2
(3)
L1,L2
(nH)
R1,R2
(
Ω
Ω
Ω
Ω
)
70
1000
120
(2)
4.7nH
100
9.1
140
1000
120
(2)
Z
0
=70
Ω
100
9.1
240
82
33
(2)
Z
0
=70
Ω
40
11
450
33
33
(2)
Z
0
=70
Ω
40
11
NOTE:
1.
Center of C9 is 3mm from the edge of the IC package
for all cases.
2.
C3 is a small-valued capacitor used to improve the
LO-RF leakage in some applications, and it has little
effect on impedance matching. C3’s value and loca-
tion depend on LO and RF frequencies and are de-
termined experimentally. In certain instances, two
common-mode capacitors to ground instead of one
single differential capacitor may provide better leak-
age suppression.
3.
The 70
Ω
microstrip transmission line TL1 and TL2
provide inductances required for matching. At lower
frequencies, external inductors are necessary.
4.
R1 and R2 set the DC current in the mixer core to the
optimum level of 50mA per side. Their values should
be well matched for best LO leakage performance.
0.1% tolerance is recommended.
5.
L1 and L2 reduce the loading effect of R1 and R2.
Their self-resonant frequency should be at least sev-
eral times the IF frequency. High quality wire-wound
type inductors are recommended. The DC resis-
tances of L1 and L2 need to be accounted for in the
selection of R1 and R2.
LO INPUT INTERFACE
The LT5579’s LO input port is internally matched from
1.1GHz to 4GHz, with a minimum return loss across
this range of about 9dB at 2.3GHz. External matching
should be used for lower LO frequencies for best per-
formance. Refer to the LT5579 datasheet for more in-
formation and impedance data.
RF OUTPUT INTERFACE
The LT5579 utilizes an internal RF transformer to step
down the mixer core output impedance to simply RF
output matching. Matching component values for sev-
eral common RF output frequencies are listed in Table
3. High quality precision microwave capacitors, such
as the AVX Accu-p series, should be used for C8 to
minimize parasitics.
Table 3. RF Output Component Values
RF Frequency (MHz)
C8 (pF)
L3 (nH)
1650
1.5
6.8
1750
1.2
6.8
1950
1
4.7
2140
0.45
3.9
2600
-
1.0
3600
0.7
0
Ω
