The CMS0004 Universal QAM/PSK Modulator is a flexible, high-performance, linear modulator core designed for a wide range of broadband applications including point-to-point and point-to-multipoint terrestrial, satellite and wireline transceiver systems.
It supports both continuous and burst-mode operation and its synchronous control interface readily accommodates physical-layer protocols that employ variable-rate frame structures.
The modulator’s symbol rate and carrier (IF) frequency are both programmable over a range extending from 0 Hertz (DC) to approximately half the applied master clock frequency.
The upper limit on master clock frequency is dependent upon the target platform (FPGA or ASIC) and process technology.
In a typical application, symbol transmit data is applied together with corresponding mapper control information.
The data passes through a FIFO buffer into the Mapper that selects the appropriate (QAM or PSK) mapping table, constellation point and transmit level from one or more lookup tables held in RAM or ROM.
The selected constellation point is up-sampled and then shaped/interpolated by a complex FIR filter using either hardwired or programmable coefficients, depending upon a synthesis option.
A separate, and optional, resampling stage provides baseband I/Q samples at the desired DAC clock frequency. The CMS0004 supports baseband I/Q and complex and real intermediate frequency (IF) outputs and provides compensation for DAC aperture distortion and DC offsets.
Register Configuration
In operation, static configuration of the modulator is performed through a small number of control ports. These would typically be driven from a bank of registers mapped into the address space of an embedded, or external, Cpu.
Parameters that may be controlled through this interface include: Symbol rate, Carrier frequency, Mapping tables, Channel filter coefficients.
