Rainbow Electronics MAX19995 - Manual (Page 25)

MAX19995
Dual, SiGe, High-Linearity, 1700MHz to 2200MHz
Downconversion Mixer with LO Buffer/Switch
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Detailed Description
The MAX19995 is a dual-channel downconverter
designed to provide 9dB of conversion gain,
+24.8dBm input IP3, +13.3dBm 1dB input compres-
sion point, and a noise figure of 9dB.
In addition to its high-linearity performance, the
MAX19995 achieves a high level of component integra-
tion. The device integrates two double-balanced mixers
for two-channel downconversion. Both the main and
diversity channels include a balun and matching cir-
cuitry to allow 50
Ω single-ended interfaces to the RF
ports and the two LO ports. An integrated single-pole,
double-throw (SPDT) switch provides 50ns switching
time between the two LO inputs, with 56dB of LO-to-LO
isolation and -31dBm 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 MAX19995’s inputs to a range of -3dBm
to +3dBm. The IF ports for both channels incorporate
differential outputs for downconversion, which is ideal
for providing enhanced 2RF-2LO performance.
Specifications are guaranteed over broad frequency
ranges to allow for use in WCDMA/LTE, DCS1800/
PCS1900 GSM/EDGE, and cdma2000 base stations.
The MAX19995 is specified to operate over an RF input
range of 1700MHz to 2200MHz, an LO range of
1400MHz to 2000MHz, and an IF range of 50MHz to
500MHz. The external IF components set the lower fre-
quency range. Operation beyond these ranges is pos-
sible; see the
Typical Operating Characteristics for
additional information. Although this device is opti-
mized for low-side LO injection applications, it can
operate in high-side LO injection modes as well.
However, performance degrades as f
LO continues to
increase. For increased high-side LO performance,
refer to the MAX19995A data sheet.
RF Port and Balun
The RF input ports of both the main and diversity chan-
nels are internally matched to 50
Ω, 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 16dB over the RF frequency
range of 1700MHz to 2200MHz.
LO Inputs, Buffer, and Balun
The MAX19995 is optimized for a 1400MHz to
2000MHz LO frequency range. As an added feature,
the MAX19995 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 50
Ω, requir-
ing 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 1k
Ω 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 MAX19995 dual-channel downconverter
consists of two double-balanced, high-performance
passive mixers. Exceptional linearity is provided by the
large LO swing from the on-chip LO buffers. When com-
bined with the integrated IF amplifiers, the cascaded
IIP3, 2RF-2LO rejection, and noise figure performance
are typically +24.8dBm, 79dBc, and 9dB, respectively.