Rainbow Electronics MAX2105 - Manual (Page 10)

MAX2102/MAX2105
Direct-Conversion Tuner ICs for
Digital DBS Applications
10 ______________________________________________________________________________________
V CC
28
27
26
25
24
23
22
21
20 56 Ω
33 Ω
19
18
17
16
15
0.22 µ F
0.22 µ F
22pF
22pF
10pF
1000pF
22 Ω
10pF
2
1
3
4
5
6
7
8
9
10
11
12
13
14
IOUT
GND
RFIN
RFIN
GND
GND
V CC
V
CC
V CC
V
CC
AGC
CONTROL
V
CC
100 Ω
LOAD
AGC
GND
GND
QOUT
V CC
V CC
V CC
V CC
PRESCALER
OUTPUT
LO
INPUT
(50
Ω
SOURCE)
MODULUS
CONTROL
V CC
MOD
PSOUT
LO
LO
GND
V CC
PSGND
V
CC
GND
IDC
IDC
QDC
QDC
10pF
1000pF
V CC
22pF
22pF
22pF
22pF
51 Ω
0.1 µ F
0.1 µ F 10pF
47 µ F
0.1 µ F
47 µ F
RF
INPUT
(50 Ω
SOURCE)
MAX2102
MAX2105
2k Ω
100 Ω
LOAD 0.1 µ F
Figure 1. Typical Operating Circuit
Detailed Description
The MAX2102/MAX2105 down-convert signals in the
range 950MHz to 2150MHz directly to baseband I/Q
signals. They are targeted for digital DBS tuner applica-
tions where a direct downconversion provides a cost
savings over prior-art, multiple-conversion approaches.
However, the MAX2102/MAX2105 are applicable to any
system requiring a broadband I/Q downconversion.
Internally, the MAX2102 and MAX2105 consist of a
broadband front-end variable gain stage, a quadrature
downconverter, an oscillator buffer, high-linearity I and
Q baseband amplifiers, and offset correction amplifiers.
The MAX2102 features a front-end AGC dynamic range
of over 50dB, while the MAX2105 provides a front-end
AGC dynamic range of over 41dB. Specifically, the
AGC control can be adjusted so that a sine wave at
RFIN ranging in power from -69dBm to -19dBm
(MAX2102) or -60dBm to -19dBm (MAX2105) will pro-
duce a sine wave at IOUT and QOUT at 500mVp-p lev-
els. The noise figure is lowest when the AGC is at its
maximum gain setting (see
Typical Operating
Characteristics ). The VSWR at RFIN is unaffected by
the AGC setting.
The local-oscillator (LO) buffer accepts an external LO
signal at LO, LO, and internally limits the signal to pro-
vide a consistent on-chip LO level. The LO input drive
level should be maintained within the specified limits
(see
Applications Information section).