Rainbow Electronics MAX19995А - Manual (Page 19)

Detailed Description
The MAX19995A is a dual-channel downconverter
designed to provide up to 8.7dB of conversion gain,
+24.8dBm input IP3, +13.5dBm 1dB input compression
point, and a noise figure as low as 9.2dB.
In addition to its high-linearity performance, the
MAX19995A achieves a high level of component inte-
gration. The device integrates two double-balanced
mixers for two-channel downconversion. Both the main
and diversity channels include a balun and matching
circuitry to allow 50Ω single-ended interfaces to the RF
ports and the two LO ports. An integrated single-
pole/double-throw (SPDT) switch provides 50ns switch-
ing time between the two LO inputs, with 48dB of
LO-to-LO isolation and -35dBm of LO leakage at the RF
port. Furthermore, the integrated LO buffers provide a
high drive level to each mixer core, reducing the LO
drive required at the MAX19995A’s inputs to a range of
-3dBm to +3dBm. The IF ports for both channels incor-
porate differential outputs for downconversion, which
are ideal for providing enhanced 2LO-2RF performance.
Specifications are guaranteed over broad frequency
ranges to allow for use in UMTS/WCDMA, LTE/WiMAX,
DCS1800/PCS1900 GSM/EDGE, TD-SCDMA, and
cdma2000 base stations. The MAX19995A is specified
to operate over an RF input range of 1700MHz to
2200MHz, an LO range of 1750MHz to 2700MHz, and
an IF range of 50MHz to 500MHz. The external IF com-
ponents set the lower frequency range (see the
Typical
Operating Characteristics for details). Operation
beyond these ranges is possible; see the Typical
Operating Characteristics for additional information.
Although this device is optimized for high-side LO
injection applications, it can operate in low-side LO
injection modes as well. However, performance
degrades as f
LO continues to decrease. For increased
low-side LO performance, refer to the MAX19995 data
sheet.
RF Port and Balun
The RF input ports of both the main and diversity chan-
nels are internally matched to 50Ω, requiring no exter-
nal matching components. A DC-blocking capacitor is
required as the input is internally DC shorted to ground
through the on-chip balun. The RF port input return loss
is typically better than 16.5dB over the RF frequency
range of 1700MHz to 2200MHz.
LO Inputs, Buffer, and Balun
The MAX19995A is optimized for a 1750MHz to
2700MHz LO frequency range. As an added feature,
the MAX19995A includes an internal LO SPDT switch
for use in frequency-hopping applications. The switch
selects one of the two single-ended LO ports, allowing
the external oscillator to settle on a particular frequency
before it is switched in. LO switching time is typically
50ns, which is more than adequate for typical GSM
applications. If frequency hopping is not employed,
simply set the switch to either of the LO inputs. The
switch is controlled by a digital input (LOSEL), where
logic-high selects LO1 and logic-low selects LO2. LO1
and LO2 inputs are internally matched to 50Ω, requiring
only 39pF DC-blocking capacitors.
If LOSEL is connected directly to a logic source, then
voltage MUST be applied to V
CC before digital logic is
applied to LOSEL to avoid damaging the part.
Alternatively, a 1kΩ resistor can be placed in series at
the LOSEL to limit the input current in applications
where LOSEL is applied before V
CC .
The main and diversity channels incorporate a two-
stage LO buffer that allows for a wide-input power
range for the LO drive. The on-chip low-loss baluns,
along with LO buffers, drive the double-balanced mix-
ers. All interfacing and matching components from the
LO inputs to the IF outputs are integrated on-chip.
High-Linearity Mixer
The core of the MAX19995A dual-channel downcon-
verter consists of two double-balanced, high-perfor-
mance passive mixers. Exceptional linearity is provided
by the large LO swing from the on-chip LO buffers.
When combined with the integrated IF amplifiers, the
cascaded IIP3, 2LO-2RF rejection, and noise-figure
performance are typically +24.8dBm, 64dBc, and
9.2dB, respectively.
Differential IF
The MAX19995A has an IF frequency range of 50MHz
to 500MHz, where the low-end frequency depends on
the frequency response of the external IF components.
Note that these differential ports are ideal for providing
enhanced IIP2 performance. Single-ended IF applica-
tions require a 4:1 (impedance ratio) balun to transform
the 200Ω differential IF impedance to a 50Ω single-
ended system. After the balun, the return loss is typical-
ly 11.5dB. The user can use a differential IF amplifier on
the mixer IF ports, but a DC block is required on both
IFD+/IFD- and IFM+/IFM- ports to keep external DC
from entering the IF ports of the mixer.
MAX19995A
Dual, SiGe, High-Linearity, 1700MHz to 2200MHz
Downconversion Mixer with LO Buffer/Switch
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