CX74017 データシートの表示（PDF） - Skyworks Solutions
部品番号
コンポーネント説明
メーカー
CX74017 Datasheet PDF : 10 Pages
| |||
On the Direct Conversion Receiver
-fIF
0 +fIF
RF cos(ωLOt)
fIF sin(ωLOt)
90°
-fLO
0 +fLO
j
-fIF
0
fIF
Σ
-fIF
0 +fIF
-fIF
0 fIF
101735A 3_071801
Figure 3. Hartley Image-Reject Architecture
RF cos(ω1t)
f2 sin(ω1t)
-f2
0 +f2
cos(ω2t)
sin(ω2t)
0
+
2×
Σ
0
-
-f1
0 +f1
j
-f2
0
f2
0
00
101735A 4_071801
Figure 4. Weaver Image-Reject Architecture
Low IF Single Conversion Receiver
Low IF single conversion, see Figure 5, is an offspring of the
DCR, and is covered in the following paragraphs. Its main
purpose is to protect the receiver from all the direct current
(DC)-related obstacles that pertain to DCR, while retaining the
DCR’s benefit of the elimination of high-Q IF filters. As its name
indicates, instead of directly converting the signal to baseband,
the LO is slightly offset from the RF carrier, typically one to two
channels. The low IF means that the fractional bandwidth of the
CX74017
IF bandpass filtering is large, making it possible to implement it
with low-Q components. The IF SAW, or crystal filter needed in
the high IF case, can be replaced with an active resistive
capacitor (RC) filter or other filter suitable for low frequency
operation that is also conducive to silicon integration. The low IF
signal may be translated to baseband through another mixer, or
preferably, in the digital domain following analog-to-digital (A/D)
conversion. Of course, this comes at the expense of faster and
higher resolution analog-to-digital converters (ADCs). If the IF
frequency is equal to only one or two channel widths, then it is
not possible to provide image-rejection at radio frequency (RF),
as the RF filter must be wide enough to pass all channels of the
system. In this case, all image rejection must come from the
quadrature downconversion to the low IF, which itself resembles
the Hartley architecture, once the baseband conversion is
added.
Image-reject
filter
RF
LNA
RF
BPF
Low IF
BPF
Low IF
f
0
f
101735A 5_072001
Figure 5. Low IF Single-Conversion Receiver
Wideband IF with double conversion
This architecture, shown in Figure 6, is very similar to the
superheterodyne. In this case, the first mixer utilizes an LO that
is at a fixed frequency, and all RF band channels are translated
to IF, retaining their positions relative to one another. The
second mixer utilizes a tunable LO, thus selecting the desired
channel to be translated to baseband. A subsequent lowpass
filter suppresses adjacent channels.
101735A
Skyworks Solutions, Inc., Proprietary and Confidential
3
July 20, 2001
Preliminary Data Subject to Change
Share Link: 