Mladen Vucic

Closed-Form Design of CIC Compensators Based on Maximally Flat Error Criterion

The simplest decimation filter is the cascaded-integrator-comb (CIC) filter. However, its magnitude response has a high passband droop, which is not tolerable in many applications. One technique for the reduction of the droop is the compensation by a filter called CIC compensator. This brief presents a method for the design of high-order finite-impulse-response CIC compensators which is based on maximally flat error criterion. The compensators coefficients are obtained by solving a linear system of equations, which is formed using a straightforward procedure. The compensators presented are suitable for application in narrow-band software radio receivers.

A class of systems with symmetric impulse response

In this paper a class of system transfer functions based on the impulse response symmetry criterion is presented. The class is obtained using nonlinear optimization procedure. Optimization of the second to tenth order system is executed. The time and frequency domain properties of obtained system or filter class are given and compared to commonly known filter approximations.

All-digital high-dynamic automatic gain control

Automatic gain control (AGC) is unavoidable part of radio receivers. Modern receivers combine analog and digital signal processing. Therefore, the AGC circuits are often implemented partially or completely in the digital domain. This paper presents the design of an all-digital high-dynamic AGC, which is suitable for high-frequency software radio receivers that use baseband signal processing. A circuit is developed which does not contain general-purpose multipliers. The design is given for arbitrary chosen input and output word length, and arbitrary chosen attack and release time. One-channel and two-channel AGC circuits are described and their FPGA implementation is discussed.

Noncausal IIR Fractional Hilbert Transformers With Equiripple or Flat Phase Response

Noncausal infinite impulse response (IIR) systems yield a much better approximation of desired response than causal systems of the same complexity. Todays technology also enables their efficient implementation. In the design of Hilbert transformers, the noncausal approach has been exploited only for conventional transformers. This brief presents a method for the design of noncausal IIR fractional Hilbert transformers based on the elliptic approximation of the desired phase shift. All-pass transformers with equiripple and flat phase responses are considered. The method is given in closed form, which makes the design robust and suitable for high-order transformers.

FPGA implementation of high-frequency software radio receiver

State-of-the-art analog-to-digital converters allow the design of high-frequency software radio receivers that use baseband signal processing. However, such receivers are rarely considered in literature. In this paper, we describe the design of a high-performance receiver operating at high frequencies, whose digital part is entirely implemented in an FPGA device. The design of digital subsystem is given, together with the design of a low-cost analog front end.

Systems with symmetric impulse response

A class of low pass systems with maximum impulse response symmetry is presented. The optimization of the rational transfer function parameters is carried out for the functions of the third to the tenth order, with two to eight zeros. The time and frequency domain properties of the systems are given and compared to the known linear phase filter approximations.

Bernoulli Low-Pass Filters

Selective filters are obtained by the approximation of the rectangular magnitude. Classic approximation methods employ polynomials or rational functions. Modern methods are based on numerical optimization. The optimization-based approach is effective and gives the designer much freedom. However, the polynomial methods are still attractive because they result in closed-form expressions and simple design procedures. This brief presents a class of low-pass filters that approximate the rectangular magnitude by using the Bernoulli polynomials. The presented filters have equiripple magnitude responses in the lower parts of the passbands, nonequiripple responses at the frequencies approaching the cutoff, and steep transition bands. Furthermore, they have low quality factors of the poles.

Filter families with minimum impulse response moments

The lowpass systems with minimum higher order moments of the impulse response are presented. The optimization of the transfer function parameters is carried out for functions ranging from the second to the tenth order, with zeros at infinity. Besides the system order, no other requirements are set to restrict the frequency domain behavior of the system. Time and frequency domain properties of the obtained systems for various moments are given and compared.

Time-Domain Synthesis of Continuous-Time Systems Based on Second-Order Cone Programming

A method for the design of continuous-time systems approximating prescribed impulse response is presented. The method is based on the least-squares error criterion. Using zero-pole-gain representation of the system, a constrained optimization problem is formed. The optimum is found by iterative procedure in which a second-order cone program is solved in each iteration. The method is applied in the design of continuous-time wavelet filters and high-voltage pulse-forming networks. It proved to be fast with low sensitivity to the iteration starting-point. Furthermore, it is suitable for the design of high-order systems.

IIR equalizer design based on the impulse response symmetry criterion

An approach for IIR equalizer design based on the impulse response symmetry is presented. Design is based on numerical optimization. General form of the objective function is given and its special cases are analyzed. It is shown that the general form gives the best results while the special cases can be more appropriate for the implementation. Practical aspects of the implementation are considered and the choice of the optimization starting point is discussed. Methods features are illustrated by an example.