0 Preface With the development of integrated circuits, a highly stable, high-precision reference voltage source has become increasingly important. Especially in D/A, A/D conversion and PLL circuits, temperature stability and accuracy are related to the accuracy and performance of the entire circuit. Most of the reference voltage sources designed today use the BJT bandgap reference structure and use the sub-threshold characteristics of MOS transistors to generate the reference voltage. However, with the development of deep sub-micron CMOS technology, the size is shrinking proportionally to the chip. The challenge of area is getting more and more serious, and the area occupied by bipolar transistors and high-precision resistors becomes a very serious problem. Here, it is proposed to generate a current proportional to the absolute temperature (PTAT) by the principle of the gate-source voltage difference of two MOS transistors operating in the saturation region, and use this current to connect an NMOS connected to a diode operating in the saturation region. The threshold voltage of the transistor is compensated to realize a low-temperature drift, high-precision reference voltage source design. 1 NMOS transistor composition The structure of two NMOS transistors M1 and M2 operating in the weak inversion region is as shown in FIG. Its output voltage V0 can be expressed as: Where: UT=kT/q; k is the Boltzmann constant; ΔV represents the error introduced by the transistor mismatch in practice, which is a constant, and its influence is ignored here. This gives you: In the formula: For NMOS transistors M1 and M2, the gate-source voltages are Vgs1 and Vgs2, respectively, then the voltage in Figure 3 is: If the MOS transistor output voltage characteristics of the two weak-inversion regions described above are used to control the gate voltages Vgs1 and Vgs2 of the two NMOS transistors operating in the saturation region, such that: Where: λ is a proportionality constant. Substituting equation (5) into equation (3) yields: For the parameter KM1, it is mainly affected by the transistor mobility λ, which is usually defined as: Where: T is the absolute temperature; α is determined by the process, and the typical value is 1.5. The formula (7) can be obtained by substituting (6): It is a temperature independent constant. According to the above analysis, this method can obtain a current I1 proportional to the absolute temperature (PTAT). The specific implementation circuit is shown in Figure 3. In the circuit of Figure 3, the four PMOS transistors M3~M6 operate in the saturation region, and their width to length ratio are the same. The two NMOS transistors M1 and M2 operate in the saturation region, and their width to length ratio is (W/L) 2 / (W / L) 1 = m. By adjusting the circuit, the four NMOS transistors M7 ~ M10 work in deep linear Area. Now let's talk about how the circuit works. For the ground voltages of points X and Y, they can be expressed as: It can be seen from equations (5) and (15) that in this circuit, the coefficients of equation (5):
Rated current of Power Filter: 0.5A~300A
Various terminals of Radio Noise Filter: wire, solder lug, stud, terminal blocks, etc
Optional medical versions(H type)
Custom specific versions available on request
Features and Benefits:
General purpose filters with good attenuation performance at frequency range 150KHz~30MHz.
Compact structure, high performance-cost ratio, easy to install, safe and reliable. FT110 and FT111 series are one-stage common mode general purpse filters with almost the same filtering effect, only slight difference according to different current.
High voltage versions above 380VAC are also available.
EMI Filter Design,General Purpose Filter,Power Filter,Radio Noise Filter Jinan Filtemc Electronic Equipment Co., Ltd. , https://www.chinaemifilter.com
It is a multiplication factor determined by temperature, and its temperature characteristics will be discussed later. 
