M21644 Datasheet, PDF (21/31 Pages) M/A-COM Technology Solutions, Inc. – 3G/HD/SD-SDI Long Reach Adaptive Cable Equalizer

Functional Descriptions
4.1.2
Adaptive Equalizer
In typical hardware mode operation, the adaptive equalization is enabled with pin.MF0 = Low (bypass disabled).
However, with pin.MF0= High, the adaptive equalization and DC restore circuit are bypassed and the input is fed
directly to the output buffers.
In software mode operation, the equalizer block can be bypassed by setting register.GenConfig.bit[5] to 1b.
The adaptive equalizer can be set to have a 6 dB gain for applications that have 400 mV_PP launch amplitude
instead of 800 mV_PP. To have this 6 dB gain, register 00h bit[2] (register.launch_ctrl) must be set to 1b.
Once there is a signal detected at the input of the equalizer, the adaptive equalizer has the ability to report what
length of Belden 1694A cable is being used. The cable length indicator results can be read on registers 05h bit[0]
and register 06h bit[7:0]. The formulas to calculate the estimated cable length are:
CL(m) = 0.625*CLI, for 0-250 m
CL(m) = 2.5*(CLI - 400) + 250, for >250 m
where CLI is the decimal value of the 9 bits from registers 05h bit[0] (msb) and register 06h bit[7:0] (lsb) and CL is
the estimated Belden 1694A cable length in meters. Table 4-1 has some of the decoded values for the cable length
indicator registers.
Table 4-1. Cable Length Indicator Decoder
CLI
Results
Estimated Cable Length*
000000000
0m
000101000
25 m
001010000
50 m
001111000
75 m
010100000
100 m
011001000
125 m
011110000
150 m
100011000
175 m
101000000
200 m
101101000
225 m
110010000
250 m
110100100
300 m
110111000
350 m
111001100
400 m
111100000
450 m
* All cable length indicator values are approximate and are not guaranteed.
21644-DSH-001-B
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