ML7404 Family LSIs
Hardware Design Manual
FEXL7404DG-03
10
4.2. Note on the VCO tank circuit
Note the following when designing the VCO tank cercuit.
1.
In order to stable VCO oscillation, the VCO tank components (L1 and C1) should be placed as close to the
IND1 (#28) and IND2 (#30) pins as possible(within 2 mm). Since the line inductance and capacitance of
PCB will effect to the oscillation frequency. Inductor L1 Should be placed closer to IND1(#28) pin or
IND2(#30) pin of ML7404 than capacitor C1. Trace length to the L1 from IND1 (#28) pin and IND2(#30)
pin of ML7404 should be same length.
2.
ML7404 maximum output power is more than50mW. As shown in the Figure 4.2.1, high output will flow
on the transmission path from PA_OUT (#20) pin. If this output affects on VCO tank circuit, it may cause
the PLL unlock. So be careful the followings:
2.1.
As shown in the Figure 4.2.2, VCO tank inductor L1 and PA choke inductor L3 should be placed so that
their positional relationship becomes the 90 degrees to avoid their coupling.
2.2.
L1 and L3 should be placed close to their connect pins of ML7404. They should not be placed close to
each other within 2 mm. Spacing between each inductors is recommended more than 8mm.
2.3.
RF maching circuit should not be close to the L1. recommends more than 6mm.
2.4.
PCB traces to the L1, C1 from VCO pins(IND1/IND2) should be symmetrical.
2.5.
L1 should be placed nearer to the VCO pins
(IND1/IND2)
than C1.
2.6.
Avoid signal line or Vdd line underneath layers of L1,C1.
Figure 4.2.1 Notes on the VCO tank circuit
Figure 4.2.2 Placement of L1 and L3
L1 and L3 should be placed so that their positional
relationship with the 90 degrees in order to avoid their
coupling.
IND1(#28)
REG_PA (#21)
PA_OUT
PA
Regulator
VC
Matching
Network
PA
L
3
～
50mW
Interference from Tx signal
IND2 (#30)
L1
C1
L3
L1
