1. Field of the Invention
This invention relates to analog-to-digital converters (ADC), and more particularly, to analog-to-digital converters using non-linear magnetoelectronic apparatus to perform comparison function.
2. Description of Related Art
High speed signal processing, used in numerous applications including telecommunications, involves conversion of analog input signals to digital data streams that are then processed by integrated circuits. The conversion process is typically performed by an analog-to-digital converter (ADC) while the converse process from digital to analog conversion is performed by a digital-to-analog converter (DAC).
The growing development of telecommunications applications that rely on bandwidth, in the range of 0.3 to 3 GHz, has generated a strong need for ADCs that operate in this frequency range, and there is an obvious advantage for ADCs that are fabricated at low cost while operating with low power. For instance, cellular phones typically operate at 2.4 GHz and every cellular phone uses an ADC with a broad band analog input. Likewise, there is a need for ADCs that operate with conversation rates of 1 Gigasamples per second (GSPS) or more to accommodate various receiver functions which are presently limited by existing ADC technology.
The existing approach to analog-to-digital (A/D) conversion is based on semiconductor technology, either CMOS, bi-CMOS, or emitter-coupled logic (ECL), while Flash ADCs are used to achieve highest conversation rates. In each cycle, n-bit digitization process requires that an input signal be sent to 2n comparators (typically 2nxe2x88x921 comparators for n-bits, and 1 comparator for signal flow). The output of the comparators is sampled and sent to decoding circuitry. The conversation speed and power dissipation is typically set by the comparators. CMOS ADCs use OP-AMP comparators, with resistors and capacitors. These passive components impose limits on speed and power. ECL ADCs typically use bipolar transistor circuits as comparators. Although they have faster conversion rates, they dissipate more power. Thus, there is a need to overcome the problems associated with prior approaches.
In the field of magnetism, a variety of magnetoelectronic devices have been developed. Most of these devices, however, utilize the bi-stable magnetization states of a ferromagnetic component for non-volatile storage of digital information. The present invention proposes using nonlinear current-voltage (I-V) characteristics of the magnetoelectronic devices as a low power alternative to existing CMOS technology in order to make them suitable converters for use as a comparator, for example, in an ADC circuits.
An apparatus and method for performing an analog to digital conversation of an input signal is described. More specifically, a magnetoelectronic device is used as a comparator in the analog to digital conversation by taking advantage of the non-linear I-V characteristics of the magnetoelectronic device.
In one aspect, the present invention discloses an analog to digital converter for converting an analog input signal to a digital output signal, comprising a comparator circuit having first to nth stages of comparators responsive to the analog input signal. Each comparator is a magnetoelectronic device having one or more ferromagnetic elements capable of being switched into a first or second magnetization states. When the amplitude of analog input signal exceeds a threshold level (IS or VS) of a comparator, the magnetization state is set to the first state and the resulting output of the comparator is a HIGH state, and vice-versa.
In another aspect, the present invention provides a method of converting an analog input signal to a digital output signal. The method includes the steps of providing a plurality of magnetoelectronic devices to perform a comparison function, each magnetoelectronic device including one or more ferromagnetic elements capable of being switched to a first or second magnetization states. Each magnetoelectronic device is enabled to set its magnetization state to a first HIGH state when the amplitude of the analog input signal exceeds a predetermined threshold, and vice-versa.
In another embodiment, the write wires through which the input current is applied to the HHE device are electrically isolated from the rest of the device and, in particular, are isolated from device output. Since the input write current is coupled inductively to the device, the capacitance is intrinsically low. It follows that a natural function of the HHE device is that of an electronic isolator. In the existing state of the art, high degrees of electrical isolation are typically provided opto-electronically. This approach is characterized by relatively low bandwidth and high operating power. Because it requires integrated light emitting diodes and photoreceptors, it is also characterized by low density of integration. A single HHE device can provide the isolation function with broad bandwidth. Because a single device is required, integration is high and power is low, and the HHE electrical isolator has significant advantages over the existing art.
While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiment, it will be apparent to those of ordinary skill in the art that many modifications may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent methods and apparatus.