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Use of Low Voltage Device in Higher Voltage Domain Regulator

IP.com Disclosure Number: IPCOM000245172D
Publication Date: 2016-Feb-16
Document File: 4 page(s) / 42K

Publishing Venue

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Abstract

As the cmos process makes progress according to Moore's law, besides the gate length narrowing, the operating voltage also goes down. However, the main voltage of the product usually needs a higher voltage (from the battery) so sometimes we need to use a low voltage device to support a higher supply voltage. This paper provides a regulation solution that uses low voltage devices to sustain a higher supply voltage. An example uses a 1.8V device to support up to 4.5V, but it could be easily extended to other applications, such as lower voltage devices or a higher supply voltage. The minimum supply voltage of the regulator is not impaired.

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Use of Low Voltage Device in Higher Voltage Domain Regulator

Abstract: As the cmos process makes progress according to Moore’s law, besides the gate length narrowing, the operating voltage also goes down.  However, the main voltage of the product usually needs a higher voltage (from the battery) so sometimes we need to use a low voltage device to support a higher supply voltage.  This paper provides a regulation solution that uses low voltage devices to sustain a higher supply voltage.  An example uses a 1.8V device to support up to 4.5V, but it could be easily extended to other applications, such as lower voltage devices or a higher supply voltage.  The minimum supply voltage of the regulator is not impaired.

As cmos processes improve, gate length gets narrower, which can save chip area, and the working voltage also goes down to save power.  However, the main voltage of the product usually needs a higher voltage, for example, if the product uses a coin battery, the voltage range is about 2.4V to 3.6V; if the product uses a Li-ion battery, the voltage range is about 2.9V to 4.2V; and for a charger the voltage is higher, say 5V or higher.  But the process could only provide a lower voltage device, for example, 1.8V, so we need to use the low voltage device to sustain higher voltage.

Below is the proposed regulator structure:

Figure 1 - Proposed regulator circuit

The proposed regulator circuit shown in Figure 1 uses M2 and M3 to help clamp the drain of the power device M1.  Current source I and the transistors in the diode connection provide the reference voltage.  For example, if the power supply voltage VDD is 4.2V, we can choose the reference on M3’s source to be about 2.5V, the voltage on M3’s gate (M1’s drain) will be about 3V (2.5V+Vth), and the gate voltage of M2 (M3’s drain) will be about 3.5V.  On the other hand, if the regulator’s output is 1.8V, the gate of M1 will be about 1.8V+Vth, so all of the transistors will be safe.  In fact, the devices M2, M3 and the...