2300 - 2700 MHz High Gain and Linearity Mixer

Description 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 base stations. 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).

Functional Description 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 balance. 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 port-to-port isolation. 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. IF Amplifier 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 or greater. 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 performance. 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.