DS30EA101: Minimum Input Sensitivity

Hi Mark,

Since the DS30EA101 is a cable equalizer, there is not a "minimum voltage swing" that must be met to determine the input sensitivity like there is for a cable driver (for example, the DS30BA101 requires at least 100 mVpp at its input). Therefore, input sensitivity is a little bit tricky to answer for Cable EQs.

The primary requirement for the DS30EA101 is that the source driving the signal going into IN+ and IN- is at least 720 mVpp (nominally 800 mVpp). From there, the "sensitivity" is determined by whether the cable EQ can provide the appropriate frequency-dependent EQ, which is as high as 50 dB at 1.5 GHz. Therefore, if the insertion loss of the cable interfacing to the DS30EA101 is too significant, the DS30EA101 will be unable to equalize the signal with zero bit errors.

Hope this helps. Please let me know if there is anything more specific about minimum input sensitivity you are looking for.

Thanks,

Michael

Hi Michael,

Could you explain in detail how to determine what the max insertion loss of the network interfacing to the DS30EA101 then? We are doing 8B/10B encoding at Nyquist frequency of 200 MHz. In a previous post, Nasser explained that the equalizer has a gain up to 16 dB at this frequency, but I'm not sure of the relationship to understand the capability of the DS30EA101.

Thanks,
Mark

Hi Mark,

The max insertion loss can be estimated by knowing two parameters:

1. EQ Gain Capability of the DS30EA101: From Nasser's previous post, the EQ capability is 16 dB at the Nyquist frequency of 200 MHz, assuming the source is outputting 800 mVpp.

2. Insertion Loss of the Cable:  This parameter is dependent on the cable length and type that you are using to interface from source to DS30EA101 input. The insertion loss can be measured with a VNA, or it can be estimated by looking at the "per 100 ft" or "per 100 m" insertion loss in the cable's datasheet.

The Cable EQ of the DS30EA101 is designed to "reverse" the effects of insertion loss that occur as a result of the cable. Since the DS30EA101 is capable of equalizing 16 dB of loss at 200 MHz, the max insertion loss of the cable interfacing to the DS30EA101 is approximately 16 dB.

The longer the cable length (assuming the cable type and vendor is the same), the sharper the slope of insertion loss vs. frequency. Therefore, you will eventually reach a cable length distance where the insertion loss at the end of the cable begins to exceed 16 dB. Beyond this length, our cable EQ is unlikely to equalize the incoming signal error-free.

In my past experience, it is usually okay to be a few dB under-equalized coming out of the Cable EQ, as typically the DS30EA101 interfaces with an FPGA or ASIC that has some EQ and retiming capability of its own. Therefore, I think that you may be able to achieve error free operation at 200 MHz Nyquist if the loss of the cable is about -17 or -18 dB.

Thanks,

Michael

Hi Michael,

An 800 mV signal with 18 dB of loss is roughly 100 mV. So the minimum voltage at the input must be at least 100 mV, at best, for the DS30EA101 to equalize a 200 MHz Nyquist (400 Mbps) signal?

Is it correct that IF we have a clean signal even after this much loss through the system, the equalizer is not necessary and that a buffer with a 100mV input sensitivity would work as well? Could you help me understand this a little more?

Thanks,

Mark