Datasheet

Maxim Integrated │ 22
MAX2022 High-Dynamic-Range, Direct Up/
Downconversion 1500MHz to 3000MHz
Quadrature Modulator/Demodulator
www.maximintegrated.com
RF Demodulator
The MAX2022 can also be used as an RF demodulator
(see Figure 4), downconverting an RF input signal directly
to baseband. The single-ended RF input accepts signals
from 1500MHz to 3000MHz. The passive mixer architec-
tureproducesaconversionlossoftypically9.2dBanda
noise figure of 9.4dB. The downconverter is optimized
forhighlinearityoftypically+39dBmIIP3.AwideI/Qport
bandwidth allows the port to be used as an image-reject
mixer for downconversion to a quadrature IF frequency.
The RF and LO inputs are internally matched to 50Ω.
Thus, no matching components are required, and only
DC-blocking capacitors are needed for interfacing.
Demodulator Output Port Considerations
Much like in the modulator case, the four baseband ports
require some form of DC return to establish a common
mode that the on-chip circuitry drives. This is achieved
by directly DC-coupling to the baseband ports (staying
within the -2.5V to +1.5V common-mode range), through
an inductor to ground, or through a low-value resistor to
ground. Figure 6 shows a typical network that would be
used to connect to each baseband port for demodulator
operation. This network provides a common-mode DC
return, implements a high-frequency diplexer to terminate
unwanted RF terms, and also provides an impedance
transformation to a possible higher impedance baseband
amplifier.
The network C
a
, R
a
, L
a
, and C
b
form a highpass/lowpass
network to terminate the high frequencies into a load
while passing the desired lower IF frequencies. Elements
L
a
, C
b
, L
b
, C
c
, L
c
, and C
d
provide a possible impedance
transformer. Depending on the impedance being trans-
formed and the desired bandwidth, a fewer number of ele-
ments can be used. It is suggested that L
a
and C
b
always
be used since they are part of the high-frequency diplexer.
If power matching is not a concern, then this reduces the
elements to just the diplexer.
Figure 4. MAX2022 Demodulator Configuration
Figure 5. Demodulator Combining Diagram
ADC
90
0
RF LO
MAX2022
DIPLEXER/
DC RETURN
MATCHING
ADC
DIPLEXER/
DC RETURN
MATCHING
3dB PAD DC BLOCK0°
3dB PAD DC BLOCK 180°
MINI-CIRCUITS
ZFSC-2-1W-S+
0° COMBINER
3dB PADS LOOK LIKE 160Ω TO GROUND
AND PROVIDES THE COMMON-MODE
DC RETURN FOR THE ON-CHIP CIRCUITRY.
I+
I-
3dB PAD DC BLOCK 0°
3dB PAD DC BLOCK 180°
MINI-CIRCUITS
ZFSCJ-2-1
MINI-CIRCUITS
ZFSCJ-2-1
Q+
Q-
90°