Digital IF Receiver
- Complete digital intermediate frequency (IF) receiver
- Quadrature numerically controlled oscillator (NCO) and digital mixer translate IF signal to baseband
- CIC and finite impulse response (FIR) filters provide decimation and filtering
- Standard processor bus interface supports programmable features
- High speed serial interface supports industry standard digital signal processing (DSP) processors
Figure 1 shows the block diagram for the digital IF receiver megafunction.
|Figure 1. Block Diagram|
The digital IF receiver megafunction combines a quadrature NCO and a digital mixer to translate the input IF signal down to baseband. Multiple Cascaded Integrator Comb (CIC) filters and a FIR filter provide bandlimiting, decimation, and interpolation to accommodate a variety of signal bandwidths. The digital IF receiver is designed to accommodate 12-bit complex data including a total of six, 4th order CIC filters, two 64-tap programmable coefficient FIR filters, a quadrature NCO, and two digital mixers to process both the in-phase and quadrature signal components.
The digital IF receiver can reduce the bandwidth and sampling rate of DSP-based receivers by pre-selecting the signals of interest. The reduction in bandwidth and sampling rate can dramatically reduce the cost and complexity of the DSP system used for downstream demodulation or other signal processing.
The Digital IF Receiver megafunction allows the designer to lower the sampling rate of the system A/D converter and still directly sample a 70 MHz IF. Through a signal processing technique known as IF under sampling, images of the desired signal are created at the sampling frequency. The digital IF receiver allows the bandwidth of interest to be selectively passed while other sampling artifacts are discarded.
The digital signal processing techniques, used in the digital IF receiver, avoid many of the undesirable effects associated with classic analog implementations. For example, digital filters do not require initial component tolerances, calibration, or preventive maintenance and do not suffer from temperature variations, or aging characteristics. Digital mixers also eliminate common analog degradations such as I/Q phase mismatch, amplitude imbalance, and DC offsets.
The FIR filters can store up to eight different sets of coefficients. The coefficient set used by the FIR filters can be dynamically changed through the processor interface. In addition, the decimation and interpolation rates of the CIC filters can be controlled by through the processor interface.
Device Utilization Example
Table 1 lists the typical device utilization results for the megafunction.
|Table 1. Typical Device Utilization for the Megafunction|
|Logic Cells||EABs (1)|
|Input sampling rate|
- EABs = Embedded array blocks
For additional information, you can contact Nova Engineering, Inc. at:Nova Engineering, Inc.
5 Circle Freeway Drive
Cincinnati, OH 45246-1105