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Boost memorised voltage range for sample-and-hold device

28 Jan 2016  | Yakov Veilkson

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The resulting circuit keeps the voltages connected to the gate and substrate for the MOS transistors of each switch within the desired 30V range (figure 3). (You derive this value from the sum of absolute-voltage values: |V1|+|V2| and |V3|=|V4|.) Voltages V1 and –V2 connect to amplifier A1, control-logic block CL1, and the substrates of the transistors of switches S1 and S2. Voltages V3 and –V4 connect to amplifier A2, control-logic block CL2, and the substrates of the transistors of switch S3.

Figure 3: You can create the changing voltages of V1 and V2 using resistor dividers R5 and R6 and R7 and R8.


You create the changing voltages of V1 and V2 using resistor dividers R5 and R6 and R7 and R8, which connect to the 30 and the –30V power supplies and the output of amplifier follower A1 (figure 3). Transistors Q1 and Q2 create the change to the power supply of amplifier A1. Voltages V1 and V2 also supply power to control-logic block CL1 and the substrates of the transistors of switches S1 and S2. CL1 comprises transistors Q11, Q12, Q15, and Q16. It creates a control signal for gates Q5 and Q6 of switch S1 and the inverse signal for gates Q8 and Q9 of S2.

1. Resistor dividers R9 and R10 and R11 and R12 connect to the 30 and the –30V power supplies, and the output of amplifier follower A2 creates the changing voltages V3 and V4. Transistors Q3 and Q4 create the change to the power supply of amplifier A2. Voltages V3 and V4 also supply power to control-logic block CL2 and the substrates of the transistors of switch S3. CL2 is made up of transistors Q13, Q14, Q17, and Q18. It creates a control signal for gates Q7 and Q10 of switch S3. Transistors Q5 through Q10 and Q11 through Q18 of CL1 and CL2, respectively, are complementary pairs of MOS logic transistors.


References
1. Velikson, Yakov, "Controlled power supply increases op amp's output-voltage range," EDN, March 15, 2007, pg 72.
2. Velikson, Yakov, and Igor Ribkin, "Analog switch, 1385288," Bulletin of Izobreteny (Copyrights and Patents), No. 12, 1988.


About the author
Yakov Veilkson contributed this article.


This article is a Design Idea selected for re-publication by the editors. It was first published on January 22, 2009 in EDN.com.


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