T-type Network Circuit of Reference Current at LOG100 Input

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The "T" type network circuit of the reference current at the LOG100 input end is shown in the figure. When LOG100 is used, very large resistance values are often required to set IREF if the reference current IREF is small. For example, if the power supply is 15V and IREF=10nA is required, RREF=15V/10nA=1500M. For such a large resistance value, it is difficult to achieve it with a single resistance. The "T" network is the solution to this problem. It decomposes the large resistance into a "T" network consisting of R1, R2, R3 and connects it to the input (14 feet). The resistance value is reduced by voltage dividing. The common resistance can achieve the IREF setting of the reference current required by a single large resistance. This method can also be used on another input (1 foot). In this way, it is important to note that the input misadjustment voltage error of internal amplifier A1 may be caused, resulting in 14 foot actual voltage not equal to zero, but equal to A1 input misadjustment voltage, and the input misadjustment voltage range is 0-5mV. The solution is to set R1, R2, R3 and keep the VT voltage greater than 5mV to ignore this effect.