mga-31189 Avago Technologies, mga-31189 Datasheet - Page 6

• Manufacturer Part Number: mga-31189
• Description: 70 To 500 Mhz Ampliier For If Applications Using The Avago Technologies Mga-31189 Ampliier
• Manufacturer: Avago Technologies

70 MHz IF Amplifier Design
When designing a DC biasing scheme, a good rule of
thumb to follow is to limit series reactance to less than
5 : and keep shunt reactance above 500 : [3]. In order
to achieve this reactance value, a minimum inductance
of 1.1 PH is needed, and typically a “PH” range inductor
will come either with a large footprint, i.e. 1206 and 1210,
or very low Q. The large size of the inductor and lower Q
is not practical for a miniature and high linearity wireless
application, so a 2012 size, 820 nH wirewound inductor
(L1), with a reasonable reactance of 361 : at 70 MHz,
was chosen. On the other hand, the high Q could be a
disadvantage in a narrowband application because of
sensitivity to part variation. Even though the reactance is
lower than the suggested value, it is sufficient to isolate
the DC supply from in-band signals. In addition, the high
Q (minimum of 23) offered by the TOKO wirewound
inductor will minimize the loss and improve OIP3 perfor-
mance.
The 0.1 PF (C4) and 2.2 PF (C5) DC bypass capacitors
short any unwanted low frequency signalsto ground, es-
Figure 11. Schematic diagram for 70 MHz design
Table 4. Component part list for the 70 MHz design
6
Reference Designator
C1
C2
C3, C6, C7
C4
C5
L1
L2
L3
RFin
C6
C=10 nF
C1
C=33 pF
Value
33 pF
22 pF
10 nF
0.1 PF
2.2 PF
820 nH
33 nH
56 nH
L3
L=56 nH
Size
0402
0402
0402
0402
0805
0805
0402
0402
MGA-31189
L1
L=820 nH
Part Number
MURATA, GRM1555C1H330JZ01
MURATA, GRM1555C1H220JZ01
MURATA, GRM155R71C103KA01
MURATA, GRM155R71C104KA88D
MURATA, GRM21BR61E225KA12L
TOKO, LLQ2012-FR82
TOKO, LL1005-FHL33NJ
TOKO, LL1005-FHL56NJ
pecially signals from the voltage supply rail. If any high
frequency signal is created or enters the DC supply, a 10
nF (C3) capacitor shorts it to ground. The 10 nF capaci-
tors are also chosen as RF coupling and DC blocks at the
input and output, as the 10 nF capacitors (Murata GRM155
Series) have a self-resonant frequency (SRF) at 75 MHz. A
coupling capacitor is selected so that its impedance is as
low as possible at the frequency of interest. The completed
70 MHz amplifier schematic is shown in Figure 11, and the
component part list is shown in Table 4.
In order to fulfill the narrowband performance at 70 MHz,
an L-C low-pass impedance matching configuration was
chosen at the input and output of the MGA-31189. A 33
pF capacitor (C1) and 56 nH (L3) inductor are used for the
input match. This combination will ensure good return
loss performance at 70 MHz. A 22 pF capacitor (C2) and
33 nH inductor (L2) is used for the output match in order
to steer the MGA-31189 impedance towards the new *
position to ensure good OIP3 performance.
Vdd
C5
C=2.2 PF
C4
C=0.1 PF
C3
C=10 nF
L2
L=33 nH
C2
C=22 pF
C7
C=10 nF
Description
Input Matching
Output Matching
RF Bypass
DC Bypass
DC Bypass
RF Choke
Output Matching
Input Matching
RFout
L