![\"Screen](\"https:\/\/www.serdesdesign.com\/home\/wp-content\/uploads\/2015\/09\/Screen-Shot-2015-09-08-at-10.44.30-AM.png\")
<\/p>\nThis section discusses typical FFE characteristics and displays. Let us know if you would like the FFE Analysis Tool enhanced with additional capability.<\/p>\n
A typical FFE for use with serial data at a bit rate (BitRate) of 6.25 Gbps has one pre-cursor and two postcursor taps. These taps are defined in units of dB emphasis with the post-cursor emphasis set to -1 dB, and the two post-cursors set to -4 and -2 dB. The overall FEE response is defined to have normalized gain of unity at its Nyquist frequency (BitRate\/2 = 3.125 GHz). Additionally, the FFE is defined to have a low pass filtering (LPF) defined with two poles at 20 GHz and 40 GHz.<\/p>\n
This FFE plus LPF design is simulated with 32 samples per bit (SamplesPerBit) to show its waveform and spectrum responses. The waveform response is defined for use with a bit pattern using a repeating set of 4 consecutive bit = 1 values followed by a set of 4 consecutive bit = 0 values (4_1_4_0). For the 6.25 Gbps data rate, one unit bit time interval (UI) is 160 psec.<\/p>\n
The FFE + LPF waveform pattern is shown here.<\/p>\n
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Under typical system usage, the bit pattern is more random using a pseudo-random bit stream (PRBS) possibly with encoding. Use of the 4_1_4_0 bit pattern for the current analysis make the emphasis characteristic of the FFE more visible. Observe that the pre-cursor and post-cursor levels are as specified. The pre-cursor transitions from level -0.269 to -0.302 resulting in -1.0 dB emphasis (20*log10(-0.269\/-0.302). The first post-cursor transitions from 0.537 to 0.339 (-4 dB). The second postcursor transitions from 0.339 to 0.269 (-2 dB).<\/p>\n
The spectrum responses for the FFE and for the FFE+LPF are shown here.<\/p>\n
![\"Screen](\"https:\/\/www.serdesdesign.com\/home\/wp-content\/uploads\/2015\/09\/Screen-Shot-2015-09-10-at-8.59.55-AM.png\")
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Observe that as specified, unity gain ( 0 dB) occurs at the Nyquist frequency (3.125 GHz). Also observe, the typical FFE spectral amplitude vs frequency oscillating from -5.4 dB to 0 dB every 6.25 GHz. The additional filter poles apply a roll-off to the FFE spectral amplitude response.<\/p>\n
The FFE Analysis Tool provides an easy exploration of the response characteristics for a defined FFE plus filter.<\/p>\n","protected":false},"excerpt":{"rendered":"
This section discusses typical FFE characteristics and displays. Let us know if you would like the FFE Analysis Tool enhanced with additional capability. A typical FFE for use with serial data at a bit rate (BitRate) of 6.25 Gbps has one pre-cursor and two postcursor taps. These taps are defined in units of dB emphasis […]<\/p>\n","protected":false},"author":2,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"nf_dc_page":"","footnotes":""},"class_list":["post-191","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.serdesdesign.com\/home\/wp-json\/wp\/v2\/pages\/191","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.serdesdesign.com\/home\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.serdesdesign.com\/home\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.serdesdesign.com\/home\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.serdesdesign.com\/home\/wp-json\/wp\/v2\/comments?post=191"}],"version-history":[{"count":1,"href":"https:\/\/www.serdesdesign.com\/home\/wp-json\/wp\/v2\/pages\/191\/revisions"}],"predecessor-version":[{"id":905,"href":"https:\/\/www.serdesdesign.com\/home\/wp-json\/wp\/v2\/pages\/191\/revisions\/905"}],"wp:attachment":[{"href":"https:\/\/www.serdesdesign.com\/home\/wp-json\/wp\/v2\/media?parent=191"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}