Boosting circuit
View Patent ↗A boosting circuit is provided which performs an appropriate boosting operation in accordance with load capacitance. In the boosting circuit, a slope control circuit is provided between a limiter circuit, which limits a high voltage obtained by a charge pump circuit to a desired boosted voltage VPP, and a discharge circuit, which makes the boosted voltage VPP drop quickly to a power supply voltage VCC after the completion of writing, to enable a boosting operation in an appropriate boosted-voltage reach time, by increasing the time taken to reach the boosted voltage VPP in the case where the load capacitance is low, while keeping the time taken to reach the boosted voltage VPP unchanged, irrespective of the presence/absence of the slope control circuit, in the case where the load capacitance is high as in the case of selecting the memory cells collectively.
1. A boosting circuit comprising:
a charge pump circuit;
a limiter circuit for limiting a high voltage obtained by the charge pump circuit to a desired boosted voltage; and
a discharge circuit for making the boosted voltage drop to a power supply voltage,
the boosting circuit further comprising a slope control circuit between the limiter circuit and the discharge circuit,
the slope control circuit including a transistor having a gate coupled to a capacitive element, the capacitive element comprising one of a capacitor or a depletion-mode transistor,
the transistor of the slope control circuit having a source connected to an output of the limiter circuit and to the capacitive element and a drain connected to an input of the discharge circuit,
the transistor of the slope control circuit being initially in an OFF state and operable to be in an ON state in response to the boosted voltage applied by the capacitive element to increase the time taken to reach the boosted voltage in the case where a load capacitance is low, and the transistor of the slope control circuit being in an ON state operable to reduce the time taken to reach the boosted voltage in the case where the load capacitance is high.
2. The boosting circuit according to claim 1 , wherein the slope control circuit includes a PMOS transistor forming the transistor of the slope control circuit, a depletion-mode NMOS transistor, the capacitive element comprising a capacitor, a current control circuit, an NMOS transistor, an inverter circuit, and a test signal input terminal,
wherein the PMOS transistor includes a source connected to the limiter circuit, a drain of the depletion-mode NMOS transistor, and to a first terminal of the capacitor, the PMOS transistor further including a drain connected to the discharge circuit and a gate connected to a source of the depletion-mode NMOS transistor, a second terminal of the capacitor, and to a first terminal of the current control circuit,
the NMOS transistor includes a source connected to a ground terminal, a drain connected to a second terminal of the current control circuit, and a gate connected to the test signal input terminal, and
wherein the test signal input terminal is further connected to a gate of the depletion-mode NMOS transistor via the inverter circuit.
3. The boosting circuit according to claim 2 , wherein the current control circuit comprises a resistive element.
4. The boosting circuit according to claim 2 , wherein the current control circuit comprises a second depletion-mode NMOS transistor,
the second depletion-mode NMOS transistor including a drain connected to the gate of the PMOS transistor, a source connected to the drain of the NMOS transistor, and a gate connected to the ground terminal.
5. The boosting circuit according to claim 2 , wherein the capacitive element comprises the depletion-mode NMOS transistor having a gate comprising the first terminal and a source and drain comprising the second terminal.
6. A boosting circuit comprising:
a charge pump circuit;
a limiter circuit for limiting a high voltage obtained by the charge pump circuit to a desired boosted voltage; and
a discharge circuit for making the boosted voltage drop to a power supply voltage,
the boosting circuit further comprising a slope control circuit between the limiter circuit and the discharge circuit,
the slope control circuit including a PMOS transistor, a depletion-mode NMOS transistor, a capacitor, a current control circuit, an NMOS transistor, an inverter circuit, and a test signal input terminal,
wherein the PMOS transistor includes a source connected to the limiter circuit, a drain of the depletion-mode NMOS transistor, and to a first terminal of the capacitor, the PMOS transistor further including a drain connected to the discharge circuit and a gate connected to a source of the depletion-mode NMOS transistor, a second terminal of the capacitor, and to a first terminal of the current control circuit,
the NMOS transistor includes a source connected to a ground terminal, a drain connected to a second terminal of the current control circuit, and a gate connected to the test signal input terminal, and
wherein the test signal input terminal is further connected to a gate of the depletion-mode NMOS transistor via the inverter circuit,
the slope control circuit operable to increase the time taken to reach the boosted voltage in the case where load capacitance is low, and to reduce the time taken to reach the boosted voltage in the case where the load capacitance is high.