1. Field of the Invention
The invention relates to a trimmer method and device for circuits, more particularly to a trimmer method and device that can facilitate adjustment of a reference signal of a circuit.
2. Description of the Related Art
In the process of fabricating integrated circuits, since it is impossible to achieve 100% precision, electrical characteristics, such as resistance and capacitance values and transistor gain, of an actual fabricated circuit usually vary from ideal values in a circuit design. The differences in electrical characteristics can result in drawbacks, such as lower operating efficiency and improper circuit operation.
Due to manufacturing, time and monetary constraints, it is not possible to conduct adjustment for each and every component of a fabricated circuit. It is noted that, for an analog circuit, what is important is to maintain the values of reference parameters, such as reference voltage and reference frequency. As to how reference parameters can be adjusted after fabrication to meet actual design requirements is an important topic in the manufacturing industry.
FIG. 1 illustrates a conventional programmable trimmer device 5 for the adjustment of a reference voltage (VF) of a target circuit 4. The trimmer device includes a series connection of three resistors 51, 52, 53, and three fuses 51A, 52A, 53A, each of which is coupled across a respective one of the resistors 51, 52, 53. By virtue of the fuses 51A, 52A, 53A, electrical conduction through each of the resistors 51, 52, 53 can be enabled or disabled, respectively. Particularly, when the fuses 51A, 52A, 53A are short-circuited, the resistors 51, 52, 53 will be bypassed, and no voltage drop will be present across the latter. On the other hand, when one of the fuses 51A, 52A, 53A is open-circuited, such as by melting, electrical conduction through the respective one of the resistors 51, 52, 53 will be enabled so as to result in a corresponding voltage drop across the same. In the following example, it is assumed that each of the resistors 51, 52, 53 has a resistance of 10 ohms, and that prior to open-circuiting of any of the fuses 51A, 52A, 53A, the current flowing through each of the fuses 51A, 52A, 53A is 1 mA. Therefore, when the reference voltage (VF) is lower than the design value by 0.02V, the reference voltage (VF) can be increased by 0.02V in the following manner: open-circuiting the fuse 53A to increase the reference voltage (VF) by 0.01V, and subsequently open-circuiting the fuse 52A to further increase the reference voltage (VF) by another 0.01V. FIG. 2 illustrates another conventional programmable trimmer device 6 which operates in a manner similar to the conventional programmable trimmer device 5 of FIG. 1. Unlike the trimmer device 5 of FIG. 1, the trimmer device 6 includes a parallel connection of three resistors 61, 62, 63, and three fuses 61A, 62A, 63A, each of which is coupled in series to a respective one of the resistors.61, 62, 63.
In the conventional programmable trimmer devices 5, 6, there is a need to couple the fuses 51A, 52A, 53A, 61A, 62A, 63A to pads (P1, P2, P3, T) . Before the packaging stage of the target circuit 4, the pad (T) is coupled to a tester (not shown), and energy in the form of a voltage or current signal for melting a selected one of the fuses is conducted through a respective one of the pads (P1, P2, P3). Because adjustment of the reference voltage (VF) in the conventional programmable trimmer devices 5, 6 requires repeated testing and fuse-melting steps, the adjustment operation is slow and inconvenient to conduct. Moreover, in order to increase the adjustment precision of the reference voltage (VF), there is a need to provide a large number of resistors and fuses, which results Ian corresponding increase in the required number of pads. The large number of allocated pads results in an undesirable increase in the size of the integrated circuit. Furthermore, because the pads have high impedance characteristics, the presence of numerous pads can lead to noise reception during testing of the target circuit 4, which can result in instability of the latter.
Therefore, the main object of the present invention is to provide a trimmer method and device that permits automatic adjustment of a reference signal.
Another object of the present invention is to provide a trimmer method and device that permits automatic selection of fuses to be melted and that further permits simultaneous melting of the selected fuses in a single fuse-melting operation so as to set a reference signal to an adjusted level.
A further object of the present invention is to provide a trimmer method and device that utilizes a relatively small number of pads to avoid an undesirable increase in size and to minimize noise reception when applied to integrated circuits.
According to one aspect of the invention, a trimmer method comprises:
a) comparing a reference signal of a target circuit with a test signal, and generating a binary count output according to result of the comparison;
b) according to logic states of bits of the binary count output, selectively enabling and disabling electrical conduction through passive components that are coupled to the target circuit and that correspond respectively to the bits of the binary count output so as to adjust the reference signal; and
c) repeating steps a) and b) by varying the binary count output until the reference signal approximates the test signal.
Preferably, after step c), fuses in a fuse set that is coupled to the passive components are melted selectively in a single fuse-melting operation so as to maintain the enabled and disabled states of electrical conduction through the passive components in order to set the reference signal to be approximate to the test signal.
According to another aspect of the invention, there is provided a trimmer device for adjusting a reference signal of a target circuit. The trimmer device comprises:
a plurality of passive components adapted to be coupled to the target circuit;
a switch device including a plurality of transistor units, each of which is coupled to a respective one of the passive components and is operable so as to selectively enable and disable electrical conduction through the respective one of the passive components for adjusting the reference signal;
a counter coupled to the switch device and operable so as to generate a binary count output that is used to selectively turn on and turnoff the transistor units of the switch device; and
a comparator circuit coupled to the counter and adapted to be coupled to the target circuit, the comparator circuit being adapted to compare the reference signal with a test signal, and generating a control signal according to result of the comparison between the reference signal and the test signal for driving the counter to vary the binary count output until the reference signal approximates the test signal.
Preferably, each of a plurality of fuses is coupled to a respective one of the passive components. The fuses are melted selectively in a single fuse-melting operation so as to maintain the enabled and disabled states of electrical conduction through the passive components in order to set the reference signal to be approximate to the test signal.