原创 Transmitter path（二） - PMA

PMA基本属于模拟范畴了，下面是Transmitter PMA的功能框图

从图中可以看到，PMA大概分三大块，Local clock divider、Serializer以及TX buffer。本地时钟分频器容易理解，而Serializer有个基本功能即Bit slipping，可以和接收端配合来调整字节、字的边界（boundary），详细内容可以查handbook。下面重点来看看40nm TX buffer的情况，框图如下：

The transmit buffer has several features to help improve the signal integrity of the system.  For example, the transmit buffer supports selectable on-chip termination in values of 85, 100, 120 and 150 ohms, depending on your target device.  OCT can be disabled but requires using an external resister.  The output differential voltage is also programmable in the range from 170 to 1350 mV, depending on your target device and your selected OCT value.  To further tailor the buffer to your system characteristics, the output buffers support programmable pre-emphasis.  The Stratix IV GX and HardCopy IV GX transmitter output driver supply voltage or VCCH can be set to 1.4 and 1.5-V. The chosen VCCH will determine the maximum data rate supported by the transmitter.  Arria II GX devices support only 1.5 V and Stratix IV GT devices support only 1.4 V.  The common mode voltage of the output for all families is fixed at 650 mV.