A detect/modulate circuit comprises a plurality of modulate resistors connected to a main resistor of a bandgap in series, and each module resistor is connected to a transistor switch in parallel, and each transistor switch is connected to a logic controller, and the logic controller is connected in sequence to a plurality of detect circuits and fuses corresponding to the quantity of the transistor switches. When the detect circuit receives a low-to-high power-on reset signal to detect whether or not the fuse is fused, the detect circuit will issue a voltage level signal “0” for the fuse being not fused or a voltage level signal “1” for the fuse being fused to the logic controller. The logic controller converts the received voltage level signal according to a logic conversion table to control the electric connection of the corresponding transistor switch, so as to fine turn the main resistance of the bandgap.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a detect/modulate circuit, and more particularly to a detect/modulate circuit using transistor switches to modulate a bandgap.

2. Description of Related Art

As the semiconductor design becomes a mainstream of the present semiconductor industry, the development of 3C and system-on-chip (SOC) becomes very popular under this trend. If low price, high performance, power saving, light, thin, short, compact and portability are taken into consideration, a more precise design technology accompanied with a better manufacturing process can achieve the request. At present, the number of transistors in per unit chip is increasing, and the integration of different elements is a significant achievement made by chip developers.

For all integrated circuits, a bandgap is needed to produce a reference voltage. The bandgap is to provide a stable temperature and voltage changed voltage. However, the bandgap will produce a deviation of output voltage due to a change of semiconductor process. To solve such output voltage deviation, related manufacturers adopt a plurality of small resistors connected to a main resistor in series. Referring toFIGS. 1 and 2, in order to compensate the deviation of output voltage, a fine tuning circuit B is connected to a main resistor A1of a bandgap A in series, and the fine tuning circuit B includes a plurality of resistors B1connected to the main resistor A1in series, and each resistor B1is connected to a fuse B2in parallel, such that each resistor B1is used for fine tuning the absolute value of the main resistor A1. The fine tuning is achieved based on whether or not the fuse B2connected to each resistor B1in parallel is fused.

But the aforesaid prior art bandgap has numerous drawback as following.

1. After the bandgap A is fabricated in a chip. To achieve both positive and negative fine tunings, all fuses B2are not fused (short-circuited) before the chip is processed. So the voltage A2of the bandgap A must be too low (as shown inFIG. 2).

2. The prior art fuse B2uses a current for fusing. When the current is controlled improperly, the bandgap A will be damaged, and thus the bandgap A will lose the function.

SUMMARY OF THE INVENTION

The present invention has been accomplished under the circumstance in view. It is therefore the main object of the present invention to use a logic controller to control the electric connection of a transistor switch, so as to fine tune the absolute value of a main resistor of the bandgap, such that the voltage outputted from the bandgap is not too low.

It is another object of the present invention to use a detect circuit to detect whether or not a fuse is fused, and output a voltage level signal to a logic controller, such that when the fuse is fused, since the current is not directly connected to the bandgap, the current of the circuit is still controlled properly and the bandgap will not be damaged or lose the function.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 3, a main resistor11of a bandgap1is connected to a detect/modulate circuit2, and the detect/modulate circuit2includes a plurality of modulate resistors21connected to the main resistor11in series, and each modulate resistor21is connected to a transistor switch22in parallel, and each transistor switch22is connected to a logic controller23, and the logic controller23is connected to a plurality of detect circuits24and fuses25corresponding to the quantity of the transistor switches22.

Referring toFIGS. 3 and 4, when the detect/modulate circuit2fine tunes a voltage (VBG)12outputted from the bandgap1, each detect circuit24will detect whether or not the fuse25is fused. If the fuse25is fused, then the detect circuit24will output a high level voltage to the logic controller23. On the other hand, if the fuse25is not fused, then the detect circuit24will output a low level voltage to the logic controller23. When the logic controller23receives a voltage level signal, then the logic controller23will convert the voltage level signal “0” or “1” according to a logic conversion table to control the corresponding transistor switch22, such that the main resistor11of the voltage generator1uses each modulate resistor21to fine tune an absolute value of the main resistor11. Therefore, the logic controller23can be used to modulate the electric connection of the transistor switches22before a chip is processed, so as to prevent the voltage12of the bandgap1being too low. Even if the current is short circuit and the control is improper, the bandgap1will not be damaged and loses the function.

Further, the transistor switch22can be an NMOS or a PMOS, and this preferred embodiment adopts the NMOS for description.

Referring toFIGS. 5 and 6, the detect circuit24includes a first inverter241, and an output end of the first inverter241is connected separately to an input end of a second inverter242and a first transistor switch245, and a source of the first transistor switch245is connected separately to an input end of a third inverter243and an output end of a fourth inverter244, and an output end of the second inverter242is connected to a second transistor246, and a source of the second transistor246is connected separately to an output end of the third inverter243and an input end of the fourth inverter244, and a drain of the second transistor246is connected to a resistor247, and the resistor247is connected to a PAD. When the fuse25is not fused, the action will be as shown inFIG. 5. By that time, the detect circuit24outputs a low level voltage to the logic controller23. When the fuse25is fused, the action will be as shown inFIG. 6. By that time, the detect circuit24outputs a high level voltage to the logic controller23, such that the logic controller23outputs “0” or “1” to the corresponding transistor switch22according to the detected voltage level signal and the logic conversion table to control the electric connection of each transistor switch22, and thus the main resistor11of the bandgap1uses each modulate resistor21to fine tune the absolute value of the main resistor11, so as to prevent any deviation.

The detect/modulate circuit of the present invention improves the prior art are described as follows.

(1) The present invention comprises a plurality of modulate resistors, and each modulate resistor is connected to the transistor switch in parallel, and each transistor switch is connected to the logic controller, such that when the logic controller receives the detected voltage level signal, the logic circuit will output “0” or “1” to the corresponding transistor switch according to the logic conversion table, so as to control the electric connection of each transistor switch and let the main resistor of the bandgap use the modulate resistors of the detect/modulate circuit to fine tune the absolute value, and thus the voltage outputted by the bandgap will not be too low.

(2) The present invention uses the detect circuit to detect whether or not the fuse is fused and outputs the voltage level signal to the logic controller to control the electric connection of each transistor switch. When the fuse is fused, since the detect circuit is not directly connected to the bandgap, the current is not controlled properly and the bandgap will not be damaged or lose the function.

(3) The present invention adds the detect circuit and the logic controller to fine tune the absolute value of the bandgap without adding any PAD or occupying too much space.

A prototype of detect/modulate circuit has been constructed with the features ofFIGS. 3˜6. The detect/modulate circuit functions smoothly to provide all of the features discussed earlier.