Floating gate analog voltage level shift circuit and method for producing a voltage reference that operates on a low supply voltage
First Claim
1. A floating gate voltage level shift circuit, comprising:
- a first floating gate for storing charge;
a second floating gate for storing charge;
a voltage shift capacitor having a first terminal coupled to the second floating gate and a second terminal; and
a differential amplifier, coupled between the first floating gate and the second floating gate, for causing the charge level on the first floating gate to be modified during a SET operation as a function of the voltage on the second floating gate;
wherein, during the SET operation, the second terminal of the voltage shift capacitor is coupled to a first predetermined voltage;
wherein, during a READ operation, the second terminal of the voltage shift capacitor is coupled to a second predetermined voltage.
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Accused Products
Abstract
A floating gate voltage level shift circuit is disclosed for generating a voltage reference which can operate on a low supply voltage Vcc by providing a circuit that enables the floating gate to be set accurately to a positive voltage during a SET operation and subsequently shifted down to a lower voltage for a READ operation. The floating gate voltage level shift circuit comprises a differential amplifier with two floating gates, a first floating gate and a second floating gate where the second floating gate is capacitively coupled to either a READ voltage or a Vshift voltage. The floating gate voltage level shift circuit operates in two primary modes, a SET operation and a READ operation. During the SET operation, the C1p capacitor of the second floating gate is connected to a Vshift voltage, rather than ground, while accurately setting the floating gate a positive voltage. The output of the differential amplifier typically swings a volt or more above and below the voltage of the second floating gate while settling to a desired voltage. During the READ operation, the C1p capacitor of the second floating gate is connected to ground, thereby causing the floating gate to shift down to a lower voltage which enables the voltage reference to work on low supply voltage.
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Citations
14 Claims
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1. A floating gate voltage level shift circuit, comprising:
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a first floating gate for storing charge; a second floating gate for storing charge; a voltage shift capacitor having a first terminal coupled to the second floating gate and a second terminal; and a differential amplifier, coupled between the first floating gate and the second floating gate, for causing the charge level on the first floating gate to be modified during a SET operation as a function of the voltage on the second floating gate; wherein, during the SET operation, the second terminal of the voltage shift capacitor is coupled to a first predetermined voltage; wherein, during a READ operation, the second terminal of the voltage shift capacitor is coupled to a second predetermined voltage. - View Dependent Claims (2, 3, 4)
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5. A floating gate voltage level shift circuit, comprising:
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a first floating gate for storing charge; a steering capacitor, coupled to the first floating gate, for controlling the charge level on the first floating gate as a function of an input set voltage that is coupled through the steering capacitor to the first floating gate during a SET operation; a second floating gate for storing charge; a voltage shift capacitor (C1p) having a first terminal coupled to the second floating gate and a second terminal coupled to a first predetermined voltage (Vfirst) during the SET operation and coupled to a second predetermined voltage (Vsecond) during a READ operation; and wherein the second predetermined voltage comprises ground. - View Dependent Claims (6, 7, 8)
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9. A floating gate voltage level shift circuit, comprising:
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a first floating gate for storing charge; a steering capacitor, coupled to the first floating gate, for controlling the charge level on the first floating gate as a function of an input set voltage that is coupled through the steering capacitor to the first floating gate during a SET operation; a second floating gate for storing charge; a voltage shift capacitor (C1p) having a first terminal coupled to the second floating gate and a second terminal coupled to a first predetermined voltage (Vfirst) during the SET operation and coupled to a second predetermined voltage (Vsecond) during a READ operation; and a feedback circuit, coupled between the first floating gate and the second floating gate, for causing the charge level on the first floating gate to be modified during the SET operation until the voltage on the first floating gate is a predetermined function of the voltage on the second floating gate. - View Dependent Claims (10)
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11. A method for operating a floating gate voltage level shift circuit having a first floating gate and a second floating gate, comprising:
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coupling a first predetermined voltage to the second floating gate during a SET operation; causing the voltage level on the first floating gate to be modified as a function of the second floating gate during the SET operation; coupling a second predetermined voltage to the second floating gate during a READ operation such that the voltage level on the second floating gate is modified; and wherein the second predetermined voltage comprises ground. - View Dependent Claims (12, 13)
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14. A method for operating a floating gate voltage level shift circuit having a first floating gate and a second floating gate coupled to a differential amplifier, comprising:
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coupling a first predetermined voltage to the second floating gate during a SET operation; causing the voltage level on the first floating gate to be modified as a function of the second floating gate during the SET operation; coupling a second predetermined voltage to the second floating gate during a READ operation such that the voltage level on the second floating gate is modified; coupling a Vset voltage to a steering capacitor, wherein the steering capacitor is coupled to said first floating gate; and measuring a Vdelta voltage which is added to the Vset voltage for one or more iterations of the SET operation to obtain a desired setting accuracy of an output voltage (Vout), wherein the value of Vdelta is equal to Vout(measured) minus Vout(desired).
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Specification