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VOLTAGE-TO-CURRENT CONVERTER

IP.com Disclosure Number: IPCOM000236901D
Publication Date: 2014-May-21
Document File: 7 page(s) / 225K

Publishing Venue

The IP.com Prior Art Database

Abstract

A novel CMOS voltage-to-current converter (VCC) circuit is proposed. The circuit is suitable for submicron technologies where the availability of a linear resistor is available. The transconductance of the converter is determined by the value of the resistor in place. Different from the classic architecture used for voltage-to-current conversion the proposed circuit does not rely on a high gain amplifier to perform the conversion. Simulation results demonstrate the performances of the VCC for a 55-nm CMOS technology.

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VOLTAGE-TO-CURRENT CONVERTER

Abstract

A novel CMOS voltage-to-current converter (VCC) circuit is proposed. The circuit is suitable for submicron technologies where the availability of a linear resistor is available. The transconductance of the converter is determined by the value of the resistor in place. Different from the classic architecture used for voltage-to-current conversion the proposed circuit does not rely on a high gain amplifier to perform the conversion. Simulation results demonstrate the performances of the VCC for a 55-nm CMOS technology.

1. Introduction

Voltage-to-Current converters are very useful circuit building blocks in analog instrumentation and electronic systems design like in the realization of filters, oscillators, amplifiers, and instrumentation.

Fig.1 shows the classic architecture of the VCC [1]. The input voltage VIN is impressed across a resistor R through a high-gain amplifier AMP and M1 which may be a NMOS or a PMOS transistor. In order to generate the output current IOUT = M . I, M3 mirrors the current I = VIN / R sensed by M2.

Fig. 1 Typical circuitry used for voltage-to-current conversion

For good linearity, a resistor with small voltage coefficient such as a poly-silicon resistor must be used. The variation of the absolute value of the output current could be as much as 25%, since it tracks the sheet resistance variation of the poly-silicon.

However, there are applications where power consumption is crucial, and an amplifier-based VCC can easily overflow the power budget. For those ones,  instead of absolute accuracy the design of a more straightforward circuit is advantageous.

In this paper an integrated converter circuit that uses resistors and CMOS transistors. The conversion accuracy is determined by one poly-silicon resistor (resistor accuracy itself).  No amplifier is used to perform the V-I conversion. Therefore, the design complexity is greatly reduced. The proposed circuit is suitable for low power medium-to-high accuracy applications.

2. Design and Implementation

Fig. 2 shows the electrical diagram of the proposed VCC.

Iref

 

Fig. 2 Electrical diagram of the proposed VCC

Considering the circuit of Figure 1 we have:

For PMOS current mirror the current IN1 and IN2 depends on Mp2 and Mp3 sizes:

(W/L)Mp1=(W/L)Mp1= Np1. (W/L)Mp3

(W/L)Mp1=(W/L)Mp2 = Np2. (W/L)Mp3

IN1 = Np1 . IN3

IN2 = Np2 . IN3                                                                                                                                                                                                                                   [1]

Considering Mn3 has always the same VGS of Mn2, if Mn3 is in saturation mode then:

IREF=Nr . IN3                                 ...