TQ9222 View Datasheet(PDF) - TriQuint Semiconductor
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TQ9222 Datasheet PDF : 16 Pages
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TQ9222
Data Sheet
LNA Input Match
The input matching network primarily determines the noise and
gain performance. Fig 4 shows a suggested input match for the
high band. The low band uses a series 1.2pF capacitor and a
shunt 10nH inductor.
1.2pF
RF
IN
Pin 2
10nH
Note: These values assume ideal components and neglect board parasitics.
The discrepancy between these values and those of the typical application
circuit are the board and component parasitics.
Fig 4. LNA Input Match
The LNA gain, noise figure and input return loss are a function
of the source impedance (Zs), or reflection coefficient (Γs),
presented to the input pin. Highest gain and lowest return loss
occur when Γs is equal to the complex conjugate of the LNA
input impedance. A different source reflection coefficient, Γopt,
which is experimentally determined, will provide the lowest
possible noise figure, Fmin.
The noise resistance, Rn, provides an indication of the sensitivity
of the noise performance to changes in Γs as seen by the LNA
input.
( ) FLNA = FMIN +
4RN ⋅
Z0 1+
Γopt − ΓS 2
Γopt 2 ⋅ 1 − Γs 2
Components such as filters and mixers placed after the LNA
degrade the overall system noise figure according to the
following equation:
FSYSTEM = FLNA + F2 − 1
GLNA
where FLNA and GLNA represent the linear noise factor and gain
of the LNA and F2 is the noise factor of the next stage. Thus, the
system noise figure depends on the highest gain and minimum
noise figure of the LNA.
Designing the input matching network involves a compromise
between optimum noise performance and best input return loss.
For example, when the TQ9222 LNA is matched for optimum
noise figure (1.35dB @ 880 MHz, and 1.45dB @ 1960 MHz),
the input return loss is only about 4dB. On the other hand,
when the LNA is matched for best return loss, the LNA noise
figure is approximately 1.95dB @ 881 MHz and 2.14dB @
1960MHz (see Table 1.)
Low Band
Freq
(MHz)
835
850
865
880
895
910
925
|Γ opt|
0.678
0.655
0.652
0.652
0.649
0.659
0.687
< Γ opt
33
34
36
38
38
40
41
Fmin
(dB)
1.34
1.38
1.36
1.35
1.36
1.35
1.35
High Band
Freq
(MHz)
1860
1960
2060
|Γ opt|
<Γ opt
Fmin
(dB)
0.557
51
1.44
0.555
54
1.45
0.532
59
1.61
Table 1. Noise Parameters
Rn
(Ω)
61.6
61.1
61.2
60.9
61.3
61.2
65.6
Rn
(Ω)
31.1
31.7
29.0
LNA Output Match
The output impedance of the high and low band LNAs, were
designed to interface directly with 50Ω terminations. This
internal match serves to reduce the number of external
components required at this port. An additional benefit accrues
as an improvement in IP3 performance, return loss and power
gain.
Low Band LNA Output
The output of the low band LNA will most often be connected to
an image stripping filter. Depending on the filter type, additional
components might be needed to present a better match to the
LNA output. The TQ9222 general applications circuit shows a
TOYOCOM (637-881A) saw filter for the low band. A series
inductor “L8”of 10nH is added to the filter input to improve the
match. This series inductor also smoothes out excessive ripple
in the filter passband improving the overall performance of the
circuit.
8
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