ADL5350 Analog Devices, Inc., ADL5350 Datasheet - Page 18

• Manufacturer Part Number: ADL5350
• Description: Lf To 4 Ghz High Linearity Y-mixer
• Manufacturer: Analog Devices, Inc.

ADL5350
2.
Typically, a band-pass network is used to pass the LO signal to
the LOIN pin. It is recommended to block high frequency
harmonics of the LO from the mixer core. LO harmonics cause
higher RF frequency images to be downconverted to the desired
IF frequency and result in a sensitivity degradation. If the
intended LO source has poor harmonic distortion and spectral
purity, it may be necessary to employ a higher order band-pass
filter network. Figure 58 illustrates a simple L-C band-pass filter
used to pass the fundamental frequency of the LO source.
Capacitor C3 is a simple DC block, while the series-inductor
(L3), along with the gate-to-source capacitance of the buffer
amplifier, form a low-pass network. The native gate input of the
LO buffer (FET) alone presents a rather high input impedance.
The gate bias is generated internally using feedback that can
result in a positive return loss at the intended LO frequency.
Table 8. Suggested RF, IF, and LO Filter Networks for Low-Side LO Injection
RF Frequency
450 MHz
850 MHz
1950 MHz
2400 MHz
1
The inductor should have a self-resonant frequency greater than the intended frequency of operation. L1 should be a high Q inductor for optimum NF performance.
Tune the LO port input network for optimum return loss.
L1
8.3 nH
6.8 nH
1.7 nH
0.67 nH
1
C1
10 pF
4.7 pF
1.5 pF
1 pF
Rev. PrE | Page 18 of 24
L2
10 nH
4.7 nH
1.7 nH
1.5 nH
If a better than −10 dB return loss is desired, it may be necessary
to add a shunt resistor to ground before the coupling capacitor
(C3) to present a lower loading impedance to the LO source.
3.
Figure 58 depicts simple LC tank filter networks for the IF and
RF port interfaces. The RF port LC network is designed to pass
the RF input signal. The series LC tank has a resonant frequency
at 1/(2π√LC). At resonance, the series reactances cancel, which
presents a series short to the RF signal. A parallel LC tank is
used on the IF port to reject the RF and LO signals. At resonance,
the parallel LC tank presents an open circuit.
It is necessary to accommodate for the board parasitics, finite Q,
and self-resonant frequencies of the LC components when
designing the RF, IF, and LO filter networks. Table 8 provides
suggested values for initial prototyping.
Design the RF and IF filter networks.
C2
10 pF
5.6 pF
1.2 pF
0.7 pF
Preliminary Technical Data
L3
10 nH
8.2 nH
3.5 nH
3.0 nH
C3
100 pF
100 pF
100 pF
100 pF