How to connect the power for VREFSD pin and anlog pin in STM32F3273 (ARM Cortex-M4) for SDADC application?
The pins VREFSD+ and VREFSD- are meant to provide an external voltage reference to the Sigma-Delta ADC. This voltage, along with the SDADC bit's resolution, gives you the overall voltage resolution of the converter. This way, the voltage resolution of an ADC is equal to the voltage reference (Vref) divided by 2 to the number of bits of the converter (16 bits in this case), following:

Q = Vref/(2^16)

where: Vref = (VREFSD+) - (VREFSD-), and Q = voltage resolution.

Then, this voltage resolution is the minimum change in voltage that the SDADC will measure. If you connect your device as depicted in your diagram (VREFSD- is usually grounded), the voltage resolution of your SDADC will be:

Q = 3.3[V]-0[V]/(2^16) = 50.35 [uV], approximately. 

This means that your system should be able to read a minimum of ~50[uV] (provided correct shielding for noise isolation), and discrete multiples of this value (100[uV],150[uV],...), all to the maximum 3.3[V] of the VREFSD+ pin. 

Additionally, you might configure your SDADC (by software) to use these external pins, an internal 1.1/1.8[V] reference or the SDADC power supply as voltage references. If you don't want to use the internal references (which should be extremely accurate), I suggest you to use an external voltage reference circuit to provide a stable voltage and ensure accurate measurements.