Abstract:
A variable circuit configuration in which each of a plurality of series connected devices is connected to a lead frame having a parallel circuit for such connected devices that can control the by-pass or use of all, some or none of the connected devices.

Description:
BACKGROUND 
     The prior art is replete with teachings of how to form on a substrate a resistor that will have a limited number of areas of differing impedance value related to one another in a binary sequence. Illustrative of these teachings are prior art U.S. Pat. Nos. 4,016,483 and 3,441,804 issued by the United States of America Patent and Trademark Office in 1977 and 1969 respectively. 
     In this prior art the intent was to provide limited infinite resolution of resistance values for circuits, and for the fine trimming of thin film resistors. In all cases, the prior art has devised such circuits so as to construct on the substrate the means of control of the implementation of the resolution of resistance values in the form of a parallel circuit of fusible links that can be opened by various techniques familiar to those skilled in the art. 
     SUMMARY 
     It is the intent of this invention to improve upon this prior art to permit more utilization of the substrate for formation of circuit devices related to each other in a predetermined manner such as, for example, a binary sequence by incorporating a novel lead frame therewith that will not only permit circuit connection but will provide for control of the use of all, some or none of the circuit devices on the substrate when connected. 
     It is a particular object of this invention to teach those skilled in the art a new structure that will permit the elimination of vast inventories of finite differing circuit devices by the use of the invention hereinafter described in reference to a preferred embodiment. 
    
    
     DRAWING DESCRIPTION 
     FIG. 1 is a schematic representation of a thin film resistance on a substrate with a lead frame connected thereto so as to provide for use thereof and for control of all, some or none of the various resistive areas of the thin film resistor; 
     FIG. 2 is a perspective blown-up view of a chip package according to this invention; and 
     FIG. 3 is a cross-sectional plan view of the chip of FIG. 2. 
    
    
     DETAILED DESCRIPTION 
     With more particular reference to FIG. 1 there is shown a substrate 10 on which has been sputtered a thin film resistance network having twelve distinct areas A, B, C, D, E, F, G, H, J, K, L and M. A lead frame with an input 12 and an output 14 is connected about the substrate to have connections 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38 and 40 connected to each of the distinct areas. In the preferred embodiment a conductive path is provided between these connections by means of structural links 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62 and 64. These links, sometimes referred to as shorting links, are typically constructed as tabs that are scribed so as to permit simple breakaway when a portion of the circuit provided by the lead frame is to be opened. This will be more particularly described with reference to FIG. 3 hereinafter. 
     As will be familiar to those skilled in the art, it is conventional to discuss thin film resistors in terms of sheet resistance, i.e., the resistance measured between terminals 12 and 14 which are molecularly bonded to the entire sides of opposite ends of the thin film resistor. The value of a thin film resistor made of a material with a given sheet resistance will be size related and is usually expressed in ohms per square. As those skilled in the art are aware, such resistors are formed and trimmed, e.g., trimmed by a laser, to create a path of connected squares whose width and length are controlled to provide a predetermined resistive impedance. This invention draws upon such prior art practices in resolving a preferred embodiment for a resistor which, according to this invention has 4096 resistance values defined a binary code comprising twelve (12) bits. 
     It should be noted at this time that the concept of this invention is available for any number of circuit devices where one has to stock several discrete variations of circuit devices, i.e., attenuators, capacitors, resistors and transistors. The description herein with specific reference to replace the fixed trim resistor inventories is adopted to provide an early disclosure of its utility without awaiting other specific circuit design and construction. It has been found that this invention will allow the user to stock a small number of individual binary selectable resistors, as they are termed in the trade, with the ability to produce resistor values from zero to 1 MEGOHM by selectively removing links 42 through 64 in accordance with a desired resistance value and then obtaining the desired binary code as follows: 
     
                                           TABLE 1__________________________________________________________________________TOTAL OHMIC RANGE VALUE 0,000 OHMS (EXAMPLE)MOST SIGNIFICANT BIT = R/2 = BIT 1LEAST SIGNIFICANT BIT = R/4096 = BIT 12BIT   1  2  3  4  5  6  7   8   9   10   11   12WEIGHT R/2    R/4       R/8          R/16             R/32                R/64                   R/128                       R/256                           R/512                               R/1024                                    R/2048                                         R/4096VALUE 5000    2500       1250          625             312.5                156.3                   78.1                       39  19.5                               9.8  4.9  2.44BINARY CODE EXAMPLE 12 BITS 42                                      64   OHMICVALUE MSB    44 46 48 50 52 54  56  58  60   62   LSB  VALUE0 =   0  0  0  0  0  0  0   0   0   0    0    0    = 01 =   0  0  0  0  0  0  0   0   0   0    0    1    = 2.4415 =  0  0  0  0  0  0  0   0   1   1    1    1    =  36.616 =  0  0  0  0  0  0  0   1   0   0    0    0    = 39.0577 = 0  0  1  0  0  1  0   0   0   0    0    1    = 14092048 = 1  0  0  0  0  0  0   0   0   0    0    0    = 50004095 = 1  1  1  1  1  1  1   1   1   1    1    1    = 9997.5__________________________________________________________________________ 1. BINARY VALUE X OHMIC VALUE OF 1 LSB = SELECTED OHMIC VALUE? 2. SELECTED OHMIC VALUE/1 LSB = BINARY VALUE? BINARY &#34;0&#34; = SHORTED BINARY &#34;1&#34; = OPEN (LINK REMOVED) 
    
     As may be appreciated this is a very limited sampling from the range of 4096 possibilities. It will be appeciated that in such code selection the links 42 through 64 are removed when a binary &#34;1&#34; is called for. 
     With reference now to FIG. 2 and encapsulated chip is shown to comprise an epoxy housing 66 with the binary code for the twelve bit design, i.e., R/2 through R/4096 preceding each tab 42 through 64. 
     This construction is opened for viewing by FIG. 3 showing the substrate 10 encircled by a flat lead frame 68 with input/output connections 12 and 14 and resistance connections, as shown. The tabs are scored as at 70 so that they can be simply broken away from the lead frame 68. With such a construction the opening of a path through a particular resistance area is not dependent on the impedance value in protection of the chip as with prior art devices that use fusible link technology on the substrate. Furthermore, the practicality to the user is enhanced by allowing the device to be factory trimmed as regards resistance value and their binary sequence with field selection the resistance combinations for a desired impedance value for the chip in use in the field. 
     Having described an operative construction for this invention with its advantages it is now desired to set forth the protection sought by these Letters Patent in the appended claims.