JPH04219011A - Oscillation circuit in semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To realize the oscillation circuit implementing the connection of a built-in feedback resistor to the oscillation circuit and the disconnection from the circuit selectively and using one oscillation circuit so as to select the built-in feedback resistor and an externally mounted feedback resistor. CONSTITUTION:A switching circuit 5 subject to on/off control by an external signal is connected across a feedback resistor 4 in an oscillation circuit in the semiconductor integrated circuit having the feedback resistor.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillation circuit in a semiconductor integrated circuit.

0002

2. Description of the Related Art FIG. 5 shows an oscillation circuit in a conventional semiconductor integrated circuit.

An inverter 13 and a feedback resistor 12 are connected in parallel between the input pad 10 and the output pad 11. Then, the output of the inverter 13 is transferred to the inverter 14.
is input to the internal cell via.

[0004] When forming an oscillation circuit in which the above-mentioned feedback resistor is externally attached, the feedback resistor 12 is omitted.

[0005]

[Problem to be Solved by the Invention] This type of oscillation circuit requires a feedback resistor, but depending on the type of circuit to be constructed, an oscillation circuit with a built-in feedback resistor in a semiconductor integrated circuit and an oscillator circuit with a built-in feedback resistor, There is an oscillation circuit that is externally attached to a semiconductor integrated circuit.

However, in the conventional oscillation circuit shown in FIG.
A feedback resistor cannot be directly attached externally to an oscillation circuit in which the feedback resistor is built into a semiconductor integrated circuit. Further, it is impossible to incorporate a feedback resistor into an oscillation circuit configured to attach the feedback resistor externally to the semiconductor integrated circuit. Therefore, in a semiconductor integrated circuit that may selectively use both oscillation circuits, two types of oscillation circuits must be formed in the semiconductor integrated circuit.

In addition, when changing an oscillation circuit with a built-in feedback resistor to an oscillation circuit that uses an external feedback resistor, it is necessary to remove the built-in feedback resistor, so the metal etc. of the wiring part of the feedback resistor must be removed with a laser beam. etc. must be used to cut.

Furthermore, since the oscillation frequency of the oscillation circuit differs depending on the resistance value of the feedback resistor, in an oscillation circuit in which the feedback resistor is built into the semiconductor integrated circuit, multiple oscillation circuits are required to obtain signals of multiple oscillation frequencies. must be formed into a semiconductor integrated circuit.

The oscillation circuit in the first semiconductor integrated circuit according to the present invention can selectively connect and disconnect the built-in feedback resistor from the circuit, and one oscillation circuit can connect the built-in feedback resistor to the circuit. An object of the present invention is to provide an oscillation circuit that allows selection of an external feedback resistor.

The oscillation circuits in the second and third semiconductor integrated circuits according to the present invention have a feedback resistor built into the semiconductor integrated circuit, and the feedback resistance value can be changed by an external signal in one oscillation circuit. The purpose is to provide an oscillation circuit that can.

[0011]

[Means for Solving the Problems] A first oscillation circuit in a semiconductor integrated circuit according to the present invention is an oscillation circuit in a semiconductor integrated circuit having a feedback resistor, in which switching is controlled on and off by an external signal across the feedback resistor. It is characterized in that the circuits are connected to each other.

A second oscillation circuit in a semiconductor integrated circuit according to the present invention is an oscillation circuit in a semiconductor integrated circuit having a feedback resistor, in which a resistor circuit including a plurality of feedback resistors connected in series serves as an input pad in the semiconductor integrated circuit. It is characterized in that it is connected to the output pad via a switching circuit that is connected between the connection points of adjacent feedback resistors and is turned on and off by a control signal from an internal register.

A third oscillation circuit in a semiconductor integrated circuit according to the present invention is an oscillation circuit in a semiconductor integrated circuit having a feedback resistor, in which a resistor circuit including a plurality of feedback resistors connected in series serves as an input pad in the semiconductor integrated circuit. It is characterized in that it is connected to the output pad via a switching circuit that is connected between the connection points of adjacent feedback resistors and is turned on and off by an external control signal.

[0014]

In the oscillation circuit in the first semiconductor integrated circuit according to the present invention, both switching circuits connected to both ends of the feedback resistor are turned on by an external signal, so that the feedback resistor is connected to the circuit.

Conversely, by turning off both switching circuits connected to both ends of the feedback resistor using an external signal, the feedback resistor is separated from the circuit.

In the oscillation circuit in the second semiconductor integrated circuit according to the present invention, the switching circuit connected between the connection point of adjacent feedback resistors and the output pad is controlled on and off by a control signal from an internal register. As a result, the resistance value of the feedback circuit changes.

In the oscillation circuit in the third semiconductor integrated circuit according to the present invention, the switching circuit connected between the connection point of adjacent feedback resistors and the output pad is turned on and off by an external control signal. , the resistance value of the feedback circuit changes.

[0018]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 4.

FIGS. 1 and 2 show a first embodiment of the invention.

FIG. 1 shows an oscillation circuit formed within a semiconductor integrated circuit.

An inverter 6 and a feedback resistor 4 are connected in parallel between the input pad 1 and the output pad 3. The output of inverter 6 is input to the internal cell via inverter 7.

As the feedback resistor 4, as shown in FIG.
A transmission gate 40 is used. That is, GND is connected to the P-channel side of the transmission gate 40, and Vcc is connected to the N-channel side, and the feedback resistor 4 is formed using the on-resistance of the transmission gate 40.

Switching circuits 5, 5 are provided at both ends of the feedback resistor 4. A transmission gate is used as each switching circuit 5, 5. The output of the inverter 8 connected to the input pad 2 is input to the P channel side of the transmission gate forming each switching circuit 5, 5. Each switching circuit 5
, 5, the output of an inverter 9 connected to the input pad 2 via an inverter 8 is input to the N-channel side of the transmission gates forming the transmission gates.

When using the feedback resistor 4, an L level signal is input to the input pad 2. Then, both switching circuits 5, 5 are turned on, and feedback resistor 4 is connected to input pad 1.
and the output pad 3. At this time, since the resistances of both switching circuits 5, 5 are much smaller than the resistance value of feedback resistor 4, the resistance values of both switching circuits 5, 5 are substantially ignored.

When using an external feedback resistor (not shown), an H level signal is input to input pad 2. Then, both switching circuits 5, 5 are turned off, and feedback resistor 4 is separated from input pad 1 and output pad 3.

According to this embodiment, one oscillation circuit can selectively use a built-in feedback resistor and an external feedback resistor.

FIG. 3 shows a second embodiment of the invention, showing an oscillation circuit formed within a semiconductor integrated circuit.

Between input pad 1 and output pad 3, 2
A series circuit consisting of two feedback resistors 4a and 4b and an inverter 6 are connected in parallel. The output of inverter 6 is input to the internal cell via inverter 7.

As feedback resistors 4a and 4b, transmission gates are used like feedback resistor 4 in FIG.

A connection point between feedback resistors 4a and 4b is connected to output pad 3 via switching circuit 5. As this switching circuit 5, a transmission gate is used. The output of the inverter 8 connected to the input pad 2 is input to the P channel side of the transmission gate constituting the switching circuit 5 . The output of an inverter 9 connected to the input pad 2 via an inverter 8 is input to the N-channel side of the transmission gate constituting the switching circuit 5 . The on-resistance of the switching circuit 5 is determined by the feedback resistors 4a and 4b.
It is so small that it can be ignored compared to the resistance value of .

When an L level signal is input to the input pad 2, the switching circuit 5 is turned on, and the feedback resistor 4a is connected between the input pad 1 and the output pad 3. At this time, the resistance of the switching circuit 5 is the feedback resistance 4
Since the resistance value of b is much smaller than that of feedback resistor 4a, the current flows through feedback resistor 4a.
and the switching circuit 5, and the resistance value of the feedback resistor is substantially the same as the resistance value of the feedback resistor 4a.

When an H level signal is input to the input pad 2, the switching circuit 5 is turned off and the feedback resistor 4a is turned off.
and 4b constitute a feedback circuit, and the resistance value of the feedback resistor is the sum of the resistance values of feedback resistors 4a and 4a.

In the second embodiment, the control signals for the switching circuit 5 are input from the outside via the input pad 2, but these control signals may also be sent from an internal register.

According to this embodiment, the resistance value of the feedback resistor can be switched in two stages, and signals with two types of oscillation frequencies can be obtained.

FIG. 4 shows a third embodiment of the present invention, and shows an oscillation circuit formed within a semiconductor integrated circuit.

Between input pad 1 and output pad 3, 4
A series circuit consisting of three feedback resistors 4a, 4b, 4c and 4d and an inverter 6 are connected in parallel. The output of inverter 6 is input to the internal cell via inverter 7.

As the feedback resistors 4a to 4d, transmission gates are used like the feedback resistor 4 in FIG. 1.

A connection point between feedback resistors 4a and 4b is connected to output pad 3 via switching circuit 5a. A connection point between feedback resistors 4b and 4c is connected to output pad 3 via switching circuit 5b. A connection point between feedback resistors 4c and 4d is connected to output pad 3 via switching circuit 5c. A switching circuit 5d is provided between the feedback resistor 4d and the output pad 3. Transmission gates are used as these switching circuits 5a to 5d.

This oscillation circuit includes a switching circuit 5a.
5d is provided with a logic circuit 20 for controlling it by external signals inputted from two input pads 2a and 2b. This logic circuit 20 includes two inverters 3
1 and 32, four AND circuits 41, 42, 43 and 44, and four inverters 51, 52, 53 and 54.

The input signal of the input pad 2a is sent to the inverter 3.
1, and the input signal of input pad 2b is sent to inverter 3.
Sent to 2. An input signal from input pad 2a and an input signal from input pad 2b are sent to AND circuit 41. A
The output of the inverter 31 and the input signal of the input pad 2b are sent to the ND circuit 42. The input signal of the input pad 2a and the output of the inverter 32 are sent to the AND circuit 43. The output of the inverter 31 and the output of the inverter 32 are sent to the AND circuit 44 .

The output of the AND circuit 41 is sent to the N channel of the transmission gate constituting the switching circuit 5d and also to the inverter 51. AN
The output of the D circuit 42 is sent to the N channel of the transmission gate that constitutes the switching circuit 5c, and is also sent to the inverter 52. The output of the AND circuit 43 is sent to the N channel of the transmission gate that constitutes the switching circuit 5b, and is also sent to the inverter 5.
Sent to 3. The output of the AND circuit 44 is sent to the N channel of the transmission gate that constitutes the switching circuit 5a, and is also sent to the inverter 54.

The output of the inverter 51 is sent to the P channel of the transmission gate constituting the switching circuit 5d. The output of the inverter 52 is sent to the P channel of the transmission gate that constitutes the switching circuit 5c. The output of the inverter 53 is sent to the P channel of the transmission gate that constitutes the switching circuit 5b. The output of the inverter 54 is the P of the transmission gate constituting the switching circuit 5a.
sent to the channel. The on-resistances of the switching circuits 5a to 5d are so small that they can be ignored compared to the resistance values of the feedback resistors 4a to 4d.

When L level signals are input to input pads 2a and 2b, the outputs of AND circuits 41, 42 and 43 become L level, and the output of AND circuit 44 becomes H level. Therefore, the four switching circuits 5a~
Of the switching circuits 5d, only the switching circuit 5a is turned on. As a result, the resistance value of the feedback circuit becomes the resistance value of the feedback resistor 4a.

When an H level signal is input to the input pad 2a and an L level signal is input to the input pad 2b, the outputs of the AND circuits 41, 42 and 44 become L level, and the AN
The output of the D circuit 43 becomes H level. Therefore, among the four switching circuits 5a to 5d, only the switching circuit 5b is turned on. As a result, the resistance value of the feedback circuit becomes the sum of the resistance values of the feedback resistors 4a and 4b.

When an L level signal is input to the input pad 2a and an H level signal is input to the input pad 2b, the outputs of the AND circuits 41, 43 and 44 become L level, and the AN
The output of the D circuit 42 becomes H level. Therefore, among the four switching circuits 5a to 5d, only the switching circuit 5c is turned on. As a result, the resistance value of the feedback circuit becomes the sum of the resistance values of the feedback resistors 4a, 4b, and 4c.

When H level signals are input to input pads 2a and 2b, the outputs of AND circuits 42, 43 and 44 become L level, and the output of AND circuit 41 becomes H level. Therefore, the four switching circuits 5a~
Of the switching circuits 5d, only the switching circuit 5d is turned on. As a result, the resistance value of the feedback circuit becomes the sum of the resistance values of the feedback resistors 4a, 4b, 4c, and 4d.

In the third embodiment, the control signals for the switching circuits 5a to 5d are transmitted to the input pads 2a and 2.
Although these control signals are input from the outside via the register b, it is also possible to send these control signals from an internal register.

According to this embodiment, the resistance value of the feedback resistor can be switched in four stages, and signals with four types of oscillation frequencies can be obtained.

[0049]

According to the oscillation circuit in the first semiconductor integrated circuit according to the present invention, by controlling both switching circuits connected to both ends of the feedback resistor, the built-in feedback resistor can be connected to the circuit and the circuit can be connected to the circuit. It is possible to selectively disconnect from the Therefore, with one oscillation circuit, it is possible to selectively use the built-in feedback resistor and the externally attached feedback resistor.

According to the second and third oscillation circuits in semiconductor integrated circuits according to the present invention, in the oscillation circuits in which the feedback resistance is built into the semiconductor integrated circuit, the feedback resistance value can be changed with one oscillation circuit.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing an oscillation circuit according to a first embodiment of the present invention.

FIG. 2 is an electrical circuit diagram showing a transmission gate used as a feedback resistor.

FIG. 3 is an electric circuit diagram showing a second embodiment of the invention and showing an oscillation circuit.

FIG. 4 is an electric circuit diagram showing an oscillation circuit according to a third embodiment of the present invention.

FIG. 5 is an electrical circuit diagram showing a conventional oscillation circuit.

[Explanation of symbols]

4 Feedback resistance 4a Feedback resistance 4b Feedback resistance 4c Feedback resistance 4d Feedback resistance 5 Switching circuit 5a Switching circuit 5b Switching circuit 5c Switching circuit 5d Switching circuit 6 Inverter

Claims (3)

[Claims] 1. An oscillation circuit in a semiconductor integrated circuit having a feedback resistor, characterized in that a switching circuit that is controlled to turn on and off by an external signal is connected to both ends of the feedback resistor, respectively. . 2. In an oscillation circuit in a semiconductor integrated circuit having a feedback resistor, a resistance circuit including a plurality of feedback resistors connected in series is connected between an input pad and an output pad in the semiconductor integrated circuit, and An oscillation circuit in a semiconductor integrated circuit, characterized in that a connection point of a resistor is connected to an output pad via a switching circuit that is controlled on and off by a control signal from an internal register. 3. In an oscillation circuit in a semiconductor integrated circuit having a feedback resistor, a resistance circuit including a plurality of feedback resistors connected in series is connected between an input pad and an output pad in the semiconductor integrated circuit, An oscillation circuit in a semiconductor integrated circuit, characterized in that a connection point of a resistor is connected to an output pad via a switching circuit that is controlled on and off by an external control signal.