12/9/2023 0 Comments Control gate transistor definition![]() ![]() ![]() These groups then connect via additional transistors to a NOR-style bit line array in the same way that single transistors are linked in NOR flash.Ī NOR flash might address memory by page and then by word. NAND flash also uses floating-gate transistors, but they connect in a way that resembles a NAND gate: several transistors connect in series, and the bit line goes low only if all the word lines are pulled high (above the transistor VT). The NOR flash moniker comes because the arrangement acts like a NOR gate: when one of the word lines (connected to the cell CG) is brought high, the corresponding storage transistor pulls the output bit line low. The other end connects directly to a bit line. In NOR flash, each cell has one end connected directly to ground. Today, there are two main types of flash, NOR and NAND. Thus current flowing or not flowing through the transistor when the intermediate voltage is asserted on the CG indicates the presence of a logical “0” or “1.” Flash memories with multi-level cells, which store multiple bits per cell, sense the amount of current flow rather than simply its presence or absence to figure out the level of charge on the FG. This means the gate stores a logical “1.” When the channel doesn’t conduct at the intermediate voltage, the FG is charged, so the gate stores a logical “0.” When the channel conducts at this intermediate voltage, it means the FG is uncharged (a charged FG would prevent conduction because the intermediate voltage is less than VT2). Flash chips today need only a single supply voltage.)Īpplying a voltage between the threshold voltages (VT1 and VT2) to the CG is all that’s needed to read a value from the transistor. (This higher voltage, often written VT2 in texts, almost always comes from an internal charge pump. This means the CG must see a higher voltage to make the channel conductive. A charge placed on the FG screens the electric field from the CG, boosting the threshold voltage (VT1) of the cell. The electrical isolation of the FG traps any electrons placed on it. The FG is completely insulated by an oxide layer and sits between the CG and the MOSFET channel. The CG resembles the gate in ordinary MOS transistors. The floating gate (FG) and the control gate (CG) control the current flowing between the source and drain. Each memory cell resembles a standard metal-oxide-semiconductor field-effect transistor (MOSFET) except that the transistor has two gates instead of one. I.e.Flash memory stores information in an array of memory cells made from floating-gate transistors. Due to the slow response of the transistor, it is possible (likely) that the input capacitor is discharged before the transistor is fully on however. Which leaves 24.5mA to discharge the input capacitor of the microcontroller, while the charging is limited to 0.5mA. The CTR has a typical value of 50%, which gives us 25mA of maximum collector current. The rise and fall times of the 4N25 are specified as typically \(2\mu s\). It is common to assume a charge time of five times the time constant, i.e. If we use a 10k pull-up, the time constant is \(70ns\). This capacitor must be charged, and the charge time is given by the time constant: Suppose the collector is connected to the input of a microcontroller (advanced gate drivers may have their own microcontrollers) with input capacitance of 7pF. ![]() The required pull-up resistor on the transistor depends on the loading imposed by the following stages in the circuit, as well as on the signal frequency. The gate resistor is split in two \(R_ = 74\Omega \] Either a positive or a negative voltage is applied to the gate with respect to the emitter, allowing fast turn on, and turn off. The two N, and P-channel MOSFET's are responsible for amplifying the control signal that enters through Rin. The figure at the right depicts the basic principle of a gate driver.
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