Modelling Flicker Phase Filter A

The simulation of filter A in the ETSI noise model, depicted as the block flickerphase in figure 7.3 will now be discussed. The transfer function for filter A in the noise model (2.1) can be expressed as  

$$H_A(s)=\prod_{n=1}^8{\frac{1}{\sqrt{7}}\left(\frac{s}{s+\alpha_ n}+\frac{\sqrt{7}\alpha_n}{s+\alpha_ n}\right)}$$ (57)

The two terms inside the brackets of (7.1) clearly correspond to first order Butterworth low and high pass filters. Thus each term of the form

$$\frac{s+\sqrt{7}\alpha_n}{s+\alpha_ n}$$

is equivalent to a cascaded $\sqrt{7}$ gain element and a low pass and high pass filter each with passband edges $\alpha_n$. Thus Filter A with the transfer function (2.1) can be modelled as a cascade of eight such low pass, high pass and gain elements.

Figures 7.4 and 7.5 show the topology of the filter A block in SPW. Figure 7.4 shows a cascade of 8 blocks each labelled unitfilt followed by a $\frac{1}{\sqrt{7}}$ gain element. Each unitfilt block is actually a low pass, high pass and $\sqrt{7}$ gain element. A typical unitfilt block is shown in figure 7.5. The passband edges for the Butterworth low and highpass filters in the cascade of eight unitfilt blocks take the values 6.72, $\frac{6.72}{7^1}$, ..., $\frac{6.72}{7^7}$Hz.

 

Figure 7.4:   Block diagram showing cascade of unitfilt blocks used to simulate filter A

 

Figure 7.5:   Block diagram of an individual unitfilt block from fig. 7.4