- LVDS接口类型
一种是HR bank的LVDS_25，Vcco=2.5V，也就是通常说的LVDS接口。
The LVDS_25 I/O standard is only available in the HR I/O banks. It requires a VCCO to be powered at 2.5V for outputs and for inputs when the optional internal differential termination is implemented (DIFF_TERM = TRUE).
一种是HP bank的LVDS，Vcco=1.8V
The LVDS I/O standard is only available in the HP I/O banks. It requires a VCCO to be powered at 1.8V for outputs and for inputs when the optional internal differential termination is implemented (DIFF_TERM = TRUE).
这句话的意思是，作为LVDS的输出或者作为输入且选择了内部终端电阻，那么VCCO的电压必须设置成1.8V（或者HR的2.5V）。
It is acceptable to have differential inputs such as LVDS and LVDS_25 in I/O banks that are powered at voltage levels other than the nominal voltages required for the outputs of those standards (1.8V for LVDS outputs, and 2.5V for LVDS_25 outputs).
However, these criteria must be met:（ug471_7Series_SelectIO， P92）
• The optional internal differential termination is not used (DIFF_TERM = FALSE, which is the default value).
• The differential signals at the input pins meet the VIN requirements in the Recommended Operating Conditions table of the specific device family data sheet
• The differential signals at the input pins meet the VIDIFF (min) requirements in the corresponding LVDS or LVDS_25 DC specifications tables of the specific device family data sheet
• For HR I/O banks in bidirectional configuration, internal differential termination is always used.
但是，如果只作为输入则不受Vcco=1.8V/2.5V限制，因为输入信号并不关心Vcco输出电压，只参考VREF电压（可选VREF_pin或者原语的 Internal_VREF）。
比如说在1.5V的bank中分配了LVDS input接口，那么，1、内部终端电阻不能选，必须外接；2、前级输出的DC特性要满足1.5V输入要求，比如上级是LVDS_25的输出VOH max 是1.675V，明显超过了1.5V电压，有反灌的风险；
- AC-couples and DC-biases the input signals
最保险的做法是采用上面的AC耦合电路，不用关心前级的直流量，只有交流信号通过，然后在输出端配置一个VCCO/2偏置电压。
总结，通常说的LVDS是2.5V的供电接口，但HP也提供1.8V的供电接口，因为DC参数完全满足。在2.5V/1.8V的bank中，可以任意配置Lvds Ourput Input，但是在其他Vcco供电bank中，就只能谨慎有条件的配置成Lvds Input，不能作为Lvds Output。