SRF-2016 SiGe IF Receiver
The Sirenza SRF-2016 is a variable gain I-Q demodulator
designed for use in receiver IF sections, as shown in the
figure below. It consists of five subcircuits: two cascaded
switched gain stages, a matched pair of mixers, and a LO
quadrature generator. This part is also available in a lower
frequency version, the SRF-1016.
The gain stages are broadband differential amplifiers each
with a digital control pin to set the gain. The gain control
pins act independently of each other. Since the amplifiers
have approximately the same gain, setting GC1 high and
GC2 low results in approximately the same gain as setting
GC1 low and GC2 high. The former setting is preferred
because it offers better noise figure. The IF input is differ-
ential with internal bias circuitry to set the common mode
voltage. The use of blocking capacitors to facilitate AC
coupling is highly recommended to avoid changing the
common mode voltage. Either input may be driven single-
ended if the other input is connected to ground through an
AC short such as a 1000 pF capacitor. This typically
results in slightly lower input P1dB.
The two matched mixers are configured with the quadra-
ture LO generator to provide in-phase and quadrature
baseband outputs. These can be fed through ADCs to a
DSP engine, or can be fed into a low frequency 90 degree
hybrid for image rejection. Alternatively, the IF signal can
be extracted from the BBI port by injecting DC into the LO
port.
The LO and IF ports offer a differential 50 ohm impedance.
The package (and in the case of the input port, the parallel
L-R network) adds inductance that tends to degrade return
loss. This can easily be matched out with a series capaci-
tor. The 8.2 pF capacitor on the evaluation board is appro-
priate for 400 MHz operation; larger capacitors should be
used for lower frequencies.
The SRF-2016 has high gain at UHF frequencies, so insta-
bility can result if there is poor power supply decoupling or
undesired coupling from the input to the output. The follow-
ing considerations should be observed when laying out a
PC board:
• Follow the general layout of the evaluation board, keep-
ing the power supply decoupling capacitors as close to
the package as possible.
• The back of the package, the two ground pins and the
decoupling capacitors should connect directly to ground,
preferably to a large dedicated ground plane.
• Use the parallel L-R circuits on the input pins.
• Ensure that the input signal tracks are routed far from
the output tracks.
• The Vcc pins are not internally connected, so all must be
connected together externally with the specified decou-
pling capacitors.
The figures on page 5 illustrate a typical SRF-2016’s per-
formance with respect to temperature. Note that these
numbers include the effect of the R-L network in the IF
port.
The frequency response of the IF and LO ports is domi-
nated by the L-R network on the input. When de-embed-
ded, the gain and P1dB response is within 0.5 dB from
200 MHz to 600 MHz.
The SRF-2016 features immunity from changes in LO
power. The gain typically changes by less than 0.6 dB over
a 6dB range of LO power. Also note the excellent I/Q bal-
ance, which typically falls within a 0.15 dB and 1.5 degree
window from 200 MHz to 600 MHz, and varies less than
0.05 dB and 0.5 degree over temperature (-40 to +85C).
The package dimensions are shown on page 3. Note that
heat is removed from the part via the back side heat slug,
so this slug must be properly soldered to a copper plane
under the part.
Evaluation boards are available for this device, and a
description of the board is shown on page 6. Note that the
evaluation board uses baluns on the I/Q outputs, and
these baluns limit the low frequency response of the
device. For true baseband operation, the baluns should be
removed, and the differential signals used directly.
LNA
RF
Filter
IF
Filter
SRF
2016
BB
Filter
BB
Filter
I
ADC
Q
ADC
Typical use for the SRF-2016 in a receiver
employing digital I/Q demodulation.
303 South Technology Court
Broomfield, CO 80021
Phone: (800) SMI-MMIC
4
http://www.sirenza.com
EDS 102137 Rev C
SIRENZA [ SIRENZA MICRODEVICES ]
