The SKY73025 is a fully integrated diversity mixer that includes
Local Oscillator (LO) drivers, an LO switch, high linearity mixers,
and large dynamic range Intermediate Frequency (IF) amplifiers.
Low loss RF baluns have also been included to reduce design
complications and lower system cost.
The SKY73025 features an input IP3 of +23.5 dBm and a Noise
Figure (NF) of 9.8 dB, making the device an ideal solution for high
dynamic range systems such as 2G/3G base station receivers.
The LO switch provides more than 45 dB of isolation between LO
inputs and supports the switching time required for GSM/EDGE
The SKY73025 is manufactured using a robust silicon BiCMOS
process and has been designed for optimum long-term reliability.
The SKY73025 diversity downconversion mixer is provided in a
compact, 36-pin 6 x 6 mm Multi-Chip Module (MCM).
The SKY73025 is a high gain diversity mixer, optimized for base
station receiver applications. The device consists of two diversity
channels (A and B), each consisting of a low loss RF balun, high
linearity passive mixer, and a low noise IF amplifier.
Two LO amplifiers (independent of channels A and B) are also
included that allow the SKY73025 to connect directly to the output
of a Voltage Controlled Oscillator (VCO). This eliminates the extra
gain stages needed by most discrete passive mixers. A Single
Pole, Double Throw (SPDT) switch has been included to select
between two different LO inputs for frequency hopping
applications (i.e., GSM).
RF Baluns and Passive Mixer
The RF baluns provide a single ended input, which can easily be
matched to 50 Ù using a simple external matching circuit. The RF
baluns offer very low loss, and excellent amplitude and phase
The high linearity SKY73025 is a passive, double balanced mixer
that provides a very low conversion loss and an excellent 3rd
Order Input Intercept Point (IIP3).
Additionally, the balanced nature of the mixer provides for high
LO Buffers and SPDT LO Switch
The LO buffers allow the input power of the SKY73025 to be in
the range of ±6 dBm. The LO section is optimized for low-side LO
injection. However, each of the two LOs can be driven over a wide
frequency range with only slight degradation in performance.
A high isolation SPDT switch allows the SKY73025 to be used for
frequency hopping applications. This switch provides greater than
45 dB of LO1 to LO2 isolation:
LO_SEL Input LO Path Selected
High LO1 (pin 19) enabled
Low LO2 (pin 27) enabled
For applications that do not require frequency hopping, LO_SEL is
fixed to one state and the appropriate LO input is used. An internal
pull-down resistor enables the LO2 input.
The SKY73025 includes high dynamic range IF amplifiers that
follow the passive mixers in the signal path. The outputs require a
supply voltage connection using inductive chokes. These choke
inductors should be high-Q and have the ability to handle 200 mA
A simple matching network allows the output ports to be matched
to a balanced 200 Ù impedance. The IF amplifiers are optimized
for IF frequencies between 50 and 500 MHz. The IF amplifiers can
be operated outside of this range, but with a slight degradation in
The RIFA and RIFB pins (29 and 17, respectively) can be
connected to external resistors (R1 and R2 – see Figure 3) to
reduce the IF amplifier bias current. When a resistor is connected
to pin 29 (R2), the Channel A IF amplifier current is reduced.
When a resistor is connected to pin 17 (R1), the Channel B IF
amplifier current is reduced. The total amount of current reduced
for Channel A and B IF amplifiers is the amount of mixer current
that is reduced.