SKY74076

The SKY74076 is a single Intermediate Frequency (IF), dual-band, receiver for Code Division Multiple Access (CDMA) and Global Positioning System (GPS) applications.

The device is a highly integrated super-heterodyne receiver. Except for the Surface Acoustic Wave (SAW) filters and matching components, the SKY74076 incorporates all the components required to implement the receiver chain, from the Low-Noise Amplifier (LNA) to the In-Phase and Quadrature (I/Q) demodulator stages. Two LNAs are in the front-end receiver: a three-step gain stage cellular LNA (high, mid, and bypass) and a high gain GPS LNA.

After RF LNA signal amplification and filtering from the antenna, the received signal of SKY74076 is mixed down from RF to IF. There are separate mixers for CDMA cellular and GPS modes. The CDMA mixer has balanced outputs for the IF SAW filters and can be combined externally to mate to a single-ended SAW filter. The GPS mixers of SKY74076 have a differential output for an external LC bandpass filter. After IF filtering, the IF signal is amplified by a Variable Gain Amplifier (VGA) and sent to an I/Q demodulator, resulting in baseband I/Q signals at the output.

The SKY74076 is also designed with two Local Oscillator (LO) input ports, one for the CDMA mixer and one for the GPS mixer. These mixers operate at different RF frequency inputs, but have the same IF frequency output. This usually refers to a single IF (SIF) plan at 183.6 MHz.

The CELL_LO signal (pin 30)  of SKY74076 provides an LO port for the CDMA cellular mixer. In the cellular band, an internal divider divides the frequency by two, which provides the LO input to the cellular mixer. Only one external VCO is required for the UHF PLL. Additionally, the mixer LO signal of SKY74076 is coupled and amplified internally, which provides another RF signal to drive the transmitter upconverter LO port.

The VGA of SKY74076 has a minimum dynamic range of 90 dB with a control voltage range of 0.5 to 2.5 V, which is common to all modes. A VHF oscillator operates with external tank circuits to provide LO frequencies for the I/Q demodulator in the cellular, PCS, and GPS modes.

The noise figure, gain, and 3rd order Input Intercept Point (IIP3) of each stage in the receiver chip are optimized to meet the system requirements for CDMA modes according to TIA/EIA-98-C. The SKY74076 design employs BiCMOS technology for low cost, high performance, and a high level of integration. A block diagram of the SKY74076 is shown in Figure 1.