METHOD AND SYSTEM FOR MODULATING FREQUENCY IN A NIGHT VISION

SYSTEM POWER SYSTEM

BACKGROUND OF THE INVENTION

[0001] Night vision systems are used in a number of applications, including military, industrial, commercial, etc. In general, the systems operate by multiplying light received at an image intensifier tube to generate a visible image. Power conservation is typically an issue with personal night vision systems that are powered by portable, battery supplies. Thus, it is beneficial to incorporate power conservation features in the night vision system in order to extend the operation of the night vision system.

BRIEF SUMMARY OF THE INVENTION

[0002] An embodiment of the invention is a night vision system including a power system having a low voltage unit coupled to a high voltage unit. The low voltage unit includes a low voltage controller and a low voltage table correlating pulse widths to step values. The low voltage unit transmits the step value to the high voltage unit in a pulse train having a period corresponding to a frequency. The high voltage unit including an opto-isolator for receiving the step value from the low voltage controller, a high voltage controller accessing a high voltage table correlating step value to pulse width and threshold. The high voltage controller generates control pulses at the frequency in response to the pulse width and the threshold.

[0003] Another embodiment of the invention is a method for controlling a night vision system. The method includes, in a low voltage unit, obtaining a desired frequency and pulse width for a control pulse and accessing a low voltage table to obtain a step value in response to the pulse width. The step value is transmitted to a high voltage unit in a pulse train having a period corresponding to the frequency. In the high voltage unit, the step value is received, a high

voltage table correlating step value to pulse width and threshold is accessed, and control pulses at the frequency are generated in response to the pulse width and the threshold.

[0004] Other embodiments of the invention include a method for controlling a night vision system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 is a block diagram of power components of a night vision system in exemplary embodiments.

DETAILED DESCRIPTION

[0006] Figure 1 is a block diagram of power components of a night vision system in exemplary embodiments. The power components include a low voltage unit 100 and a high voltage unit 200. The low voltage unit 100 and the high voltage unit 200 operate with a significant volt Figure 1 is a block diagram of power components of a night vision system in exemplary embodiments. The power components include a low voltage unit 100 and a high voltage unit 200. The low voltage unit 100 and the high voltage unit 200 operate with a significant voltage potential difference between them. The low voltage unit 100 includes a low voltage controller 102 in communication with low voltage electronics 104 and an opto-isolator 202 in the high voltage unit 200. The low voltage electronics 104 may include amplifiers, inverters, transformers, etc. A battery 108 is coupled to the low voltage electronics 104 to provide power to the high voltage unit 200.

[0007] The low voltage controller 102 may be a general-purpose microprocessor executing a computer code contained on a storage medium. Alternatively, the low voltage controller 102 may be implemented using a wide variety of other technologies including a special purpose computer, a computer system including a microcomputer, mini-computer or mainframe for example, a programmed microprocessor, a micro-controller, a peripheral

integrated circuit element, a CSIC (Customer Specific Integrated Circuit) or ASIC (Application Specific Integrated Circuit) or other integrated circuit, a logic circuit, a digital signal processor, a programmable logic device such as a FPGA, PLD, PLA or PAL, or any other device or arrangement of devices that is capable of implementing the steps of processes in embodiments of the invention.

[0008] The low voltage controller 102 interfaces with a low voltage table 103 to retrieve a step value that is transmitted to the high voltage unit as described in further detail herein. Low voltage table 103 may be a look-up table through which the low power controller 102 obtains a step value based on a desired pulse width. Low voltage table 103 may be stored in memory located in low power controller 102 or a separate device accessible by low power controller 102.

[0009] The opto-isolator 202 serves as an optically isolated one-way data link used to transfer information from the low voltage unit 100 to the high voltage unit 200. One of the information items is a step value, which corresponds to a desired pulse width. The step value represents the desired pulse width to be used in the high voltage unit and is obtained from low voltage table 103 as described in further detail herein. In an exemplary embodiment, the step value is an N-bit digital word representing the desired pulse width. Once the step value is received by the high voltage unit 200, the high voltage unit 200 generates a control pulse with a duration between 1250 μs and 300 ns by accessing high voltage table 203 with the step value. The opto-isolator 202 receives the step value and provides the step value to the high voltage controller 204. The high voltage controller 204 uses the step value to interface with pulse shaping module 210 to control high voltage power electronics 206 that bias the night vision system.

[0010] The high voltage controller 204 interfaces with high voltage table 203 to retrieve a pulse width in response to the step value transmitted from the low voltage unit 100. High voltage table 203 may be a look-up table through which the high power controller 204 obtains a pulse width based on the received step value. High voltage table 203 may be stored in memory

located in high power controller 204 or a separate device accessible by high power controller 204.

[0011] A conventional method of defining a pulse width is to create a digital word where each count equals the minimum resolution. In power system of Figure 1 with a minimum pulse resolution of Ins and a maximum value of 1250μs, a digital word scaled at 1 count = Ins would need to be capable of storing 1,250,000 counts to accommodate the desired resolution and maximum range. This requires a 21 bit digital word to represent 1,250,000 counts.

[0012] As noted above, a constraint of the night vision power system is power consumption. Sending 21 data bits drives up system power due to the energy required to drive the opto-transmitter for that many bits as well as the real-time power consumption needed during the data transmission and reception.

[0013] As described above, the low voltage unit accesses low voltage table 103 to obtain a step value corresponding to a desired pulse width. The step value uses a reduced number of bits to communicate the pulse width. Exemplary step values and pulse widths are shown in Table 1. The pulse values start at the maximum, e.g., 1250μs and go down by a percentage (e.g., 2.5%) in each step. A total of 336 steps are defined from 0 to 335 corresponding to pulse widths from 1250μs to 319ns.

Table 1 - Pulse Widths

[0014] In operation, the low voltage controller 102 determines the desired pulse width and accesses low voltage table 103 to determine the appropriate step value. The low voltage unit 100 sends a digital word representing the step value by accessing low voltage table 103 indexing the desired pulse width to the step value. Accordingly, instead of sending the pulse width value across the data link, a step value from Table 1 is sent. Using this method, the data transmitted across the data link need only be 10 bits as opposed to 21 bits if the pulse width value is sent. Nine bits are used to send the step value and a tenth bit may be included as a steering bit to direct the 9 bit word to the appropriate high power circuitry. The power electronics 206 include circuitry for controlling both DC levels and voltage gating on the night vision MCP. The steering bit indicates that the step value is for the gated voltage. Sending 10 bits results in a 2x power reduction and transmission time reduction as compared to sending 21 bits.

[0015] The low voltage controller 102 sends the step value to the high voltage controller 204 through opto-isolator 202. The high voltage controller 204 accesses high voltage table 203, which is a local copy of low voltage table 103, and determines the pulse

width corresponding to the received step value. The high voltage controller 202 causes this pulse width to be produced though pulse shaping module 210, which in-turn drives high voltage electronics 206 through a control pulse. For example, the high voltage electronics 206 may include a digital to analog converter and several analog output functions, all of which reside in the high voltage block.

[0016] This communication protocol uses less power and communication time than standard digital communication protocols. Using tables 103 and 203 provides fast, low power operation. The main idea is to use a correlation table based upon a 2.5% change between steps, which results in a logarithmic scaling relationship between inputs to output.

[0017] In exemplary embodiments, the low voltage controller can also alter the frequency of the control pulse output by the pulse shaping module 210 to provide frequency agility. This allows the frequency of the control pulses to be altered. It is desirable to modulate frequency of the system in order to eliminate beat frequencies with ancillary equipment such as video displays. Conventional techniques require a look-up table for each frequency in order to provide the ability to alter frequency with constant duty cycle. This results in an increased size in look-up tables, and an increased number of bits needed to access the look-up tables. This has a significant impact on power consumption and cost.

[0018] In embodiments of the invention, the low voltage unit 100 transmits the step value at varying rates in order to provide frequency agility. The low voltage controller 102 determines the pulse width and frequency for the control pulse. As described above, the step value corresponding to the desired pulse width is obtained from table 103. The low voltage controller 102 then sends the step values at the rate of the period of the frequencies of 1/T ₁ , and/or l/f ₂ , and/or l/f ₃ , etc.

[0019] The high voltage unit 200 produces a single output control pulse every time it receives a step value. So if high voltage unit 200 receives step values at time periods of 1/fi

then the output pulses will be at a frequency of U ₁ and so on. When the high voltage controller 204 receives the step value, the high voltage controller 204 sends the step value to table 203 gets back two pieces of data: 1) the pulse width and 2) a threshold voltage value to be used by the pulse shaping module 210 in creating the control pulse. The threshold value is used to create the control pulse as described in co-pending US patent application serial number , entitled METHOD AND SYSTEM FOR CONTROLLING PULSE

WIDTH IN A NIGHT VISION SYSTEM POWER SYSTEM filed concurrently with this application, the contents of which are incorporated herein by reference. The threshold value is used by the pulse shaping module 210 to generate control pulses having the desired resolution.

[0020] The frequencies selected by the low voltage unit 100 also vary from a maximum value to a minimum value in a logarithmic relationship matching the logarithmic relationship of the step values. That is, in the example discussed above, the frequencies selected by the low voltage unit vary from maximum to minimum in 2.5% decrements. The significance of this relationship is that if both the pulse widths and frequencies are of the same logarithmic scaling relationship, i.e., each varies by 2.5%, then only one number (i.e., the step value) needs to be transmitted over the optical link. This reduces the data transmission across the optical link and reduces power consumption. .

[0021] As described above, the embodiments of the invention may be embodied in the form of processor-implemented processes and apparatuses for practicing those processes. Embodiments of the invention may also be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a processor, the processor becomes an apparatus for practicing the invention. The present invention can also be embodied in the form of computer program code, for example, whether stored in a storage medium, loaded

into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits.

[0022] While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed for carrying out the invention, but that the invention will include all embodiments falling within the scope of the appended claims.