JP2000174556A - Feedback resistor in oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a feedback resistor with a stable feedback resistance for a highly reliable oscillation circuit by reducing dependence of the feedback resistor of the oscillation circuit integrated in an LSI on a power supply voltage. SOLUTION: A P-channel transistor(TR) (PMOS) 11 and an N-channel TR (NMOS) 6 are placed in parallel in an analog SW 5, and a voltage divided from a power supply voltage by a TR 8, 12 that is normally conductive and a resistive element 7, 13 is given to a gate electrode of the P-channel TR (PMOS) 11 and N-channel TR (NMOS) 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a feedback resistor in an oscillation circuit.

[0002]

2. Description of the Related Art Heretofore, there have been the following oscillation circuits for ceramic oscillators.

FIG. 4 is an oscillation circuit diagram for such a conventional ceramic oscillator.

In FIG. 1, reference numeral 101 denotes an input terminal (XT).
Terminals), 102 are inverted output terminals (XT inverted terminals), 10
3 is the first inverter, 104 is the second inverter, 1
05 is a feedback resistor (1 MΩ) in the oscillation circuit, 106 is an oscillator, and 107 and 108 are capacitors.

As shown in FIG. 1, in a conventional circuit, feedback resistors 105 in an oscillation circuit are individually provided. The feedback resistor 105 is as large as 1 MΩ, and requires a large area to obtain a high resistance value. Further, its manufacture is complicated, and its operation is difficult and costs increase.

On the other hand, recently, the circuit portion is being manufactured at the same time inside the LSI as much as possible, and the feedback resistance (1 MΩ) in the oscillation circuit is being formed as follows.

FIG. 5 is an oscillation circuit diagram for such a conventional LSI ceramic oscillator. The same parts as those shown in FIG. 4 are denoted by the same reference numerals, and their description is omitted.

In FIG. 5, an analog switch (analog SW) 110 is provided in place of the feedback resistor (1 MΩ) 105 in the oscillation circuit shown in FIG. 4, and a gate electrode 111 of an N-type transistor NTr of the analog switch 110 is provided. Is supplied with the power supply voltage Vdd and its analog switch 1
The gate electrodes 112 of the ten P-type transistors PTr are connected to the ground (G), respectively.
Is always in the ON state, and the equivalent resistance value at that time (1M
Ω) is inserted into the oscillation circuit.

That is, a conventional oscillation circuit for a ceramic oscillator often has a built-in feedback resistor inside the LSI as shown in FIG. 5, and its configuration is different from that shown in FIG. This has the advantage that the chip area can be reduced.

[0010]

However, when the gate voltage is fixed as in the feedback resistor of the conventional oscillation circuit shown in FIG. 5, the gate voltage of the N-type transistor NTr (NMOS) of the analog SW 110 and the P-type The gate voltage of the transistor PTr (PMOS) greatly depends on the power supply voltage Vdd, and the resistance value varies greatly with respect to the power supply voltage Vdd.

This point will be described in detail by taking the NMOS shown in FIG. 6 as an example.

The equivalent resistance when the NMOS is turned on is V
It becomes smaller as gs is larger. Supply voltage Vd to gate voltage
When d is directly connected, Vgs = Vdd, and Vdd
, The value of the NMOS resistance greatly changes.

For example, when Vdd = 5V, the resistance component is 1M
When Ω Vdd = 2 V, the resistance is 4 MΩ.

That is, the tendency is as follows: Vdd high → gate voltage high → analog SW resistance small, and Vdd low → gate voltage low → analog SW resistance large.

In an LSI, the power supply voltage Vdd is designed in consideration of the entire circuit configuration, and a wide range of Vdd is considered. In other words, when the Vdd range of the LSI is wide, for example, when Vdd is 2 to 5.5 V, the feedback resistance of the oscillation circuit greatly varies as described above, causing a problem.

The present invention eliminates the above problems, reduces the dependence of the feedback resistance of an oscillation circuit incorporated in an LSI on the power supply voltage, and reduces the feedback resistance in a highly reliable oscillation circuit having a stable feedback resistance. The purpose is to provide.

[0017]

In order to achieve the above object, the present invention provides: [1] In a feedback resistor in an oscillation circuit, a feedback resistor of the oscillation circuit is constituted by a transistor, and a gate electrode of the transistor is It is configured to apply a voltage divided by a transistor and a resistance element that are always on.

[2] In the feedback resistor in the oscillation circuit according to [1], the transistor includes a P-type transistor and an N-type transistor arranged in parallel, and the gate electrodes of the P-type transistor and the N-type transistor are always connected to the gate electrodes. The configuration is such that a voltage divided by the on-state transistor and the resistance element is applied.

[3] The feedback resistor in the oscillation circuit according to [1], wherein a voltage divided by an N-type transistor and a resistance element is applied to the transistor.

[4] The feedback resistor in the oscillation circuit according to [1], wherein a voltage divided by a P-type transistor and a resistance element is applied to the transistor.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a feedback resistor circuit diagram in an oscillation circuit showing a first embodiment of the present invention.

In this figure, 1 is an input terminal (XT terminal), 2 is an inverted output terminal (XT inverted terminal), 3 is a first inverter, 4 is a second inverter, 5 is an analog switch (analog SW), 6 is the analog switch N
Type transistors NTr (NMOS), 7 and 13 are resistance elements, and 8 is an N-type transistor NTr (NM
OS), 9 and 14 are ground (G), 11 is a P-type transistor PTr (PMOS) of an analog switch, and 12 is a P-type transistor PTr (PMOS) which is always on.

In this embodiment, the analog SW 5 includes a P-type transistor (PMOS) 11 and an N-type transistor (NM).
OS) 6 are provided side by side, and this P-type transistor (PMO
The S) 11 and the gate electrode of the N-type transistor (NMOS) 6 are configured to apply a voltage divided by the transistors 8 and 12 and the resistance elements 7 and 13 which are always on.

According to this embodiment, in FIG.
If s is expressed as a ratio to Vdd, it is always "1". When the Vdd is high, the circuit inserted in the gate section
When the ratio is made small, Vgs is made small, and as a result, the resistance value is made large. When Vdd is low, the ratio is made large, Vgs is made large, and as a result, the resistance value is made small. be able to. Therefore, the problem of the conventional example shown in FIG.
The variation due to dd can be suppressed.

According to this embodiment, FIG.
In the case of the NMOS shown in (1), when the voltage of S (source) is low, Vgs becomes large and the resistance value becomes small. When the voltage of S is high, Vgs becomes small and the resistance value becomes large. When the voltage of S is 4.3 V or more, Vgs becomes 0.7 V or less,
The resistance value is infinite, that is, open.

That is, in the case of the NMOS shown in FIG. 2 to be described later, the function of the feedback resistor is not performed when the voltage of D (drain) and S is near Vdd.

On the other hand, in the case of the PMOS shown in FIG. 3, which will be described later, on the other hand, the function as a feedback resistor is not achieved near GND.

Therefore, according to the first embodiment of the present invention, N
Since the MOS and the PMOS are connected in parallel, the region where the resistance value becomes infinite can be complemented with each other, and there is an advantage that the function as a feedback resistor can be performed in any voltage range.

FIG. 2 is a feedback resistor circuit diagram in an oscillation circuit showing a second embodiment of the present invention.

In this figure, 21 is an input terminal (XT terminal), 22 is an inverted output terminal (XT inverted terminal), 23 is a first inverter, 24 is a second inverter, and 25 is connected between input and output terminals. N-type transistor NTr (NMO
S), 26 is a gate electrode of NTr 25, 27 is a resistance element having one end connected to power supply voltage Vdd and the other end connected to gate 26 of NTr 25, 28 is the other end of resistance element 27 and gate 2
N-type transistor NTr that is always on and is connected to
(NMOS) 29 is a ground (G) connected to one end of the NTr 28.

According to the second embodiment, a feedback resistance value can be obtained with a simple circuit configuration. However, as described above, when the voltage of S (source) is 4.3 V or more, Vg
Since s becomes 0.7 V or less and the resistance value becomes infinite,
Care must be taken in the selection of the voltage range to avoid such regions.

FIG. 3 is a feedback resistor circuit diagram in an oscillation circuit showing a third embodiment of the present invention.

In this figure, 31 is an input terminal (XT terminal), 32 is an inverted output terminal (XT inverted terminal), 33 is a first inverter, 34 is a second inverter, and 35 is connected between input and output terminals. P-type transistor PTr (PMO
S) and 36 are gate electrodes of the PTr 35, and 37 is a normally-on P-type transistor P connected to the power supply voltage Vdd.
Tr (PMOS), 38 is a gate electrode of the PTr 37, 39 is a ground connected to the gate 38, 40 is a resistor connected to the PTr 37 and the gate electrode 36,
Reference numeral 41 denotes a ground connected to the other end of the resistance element 40.

Also according to the third embodiment, a feedback resistance value can be obtained with a simple circuit configuration. However, as described above, since the voltage of D (drain) and S does not function as a feedback resistor near GND, it is necessary to pay attention to the selection of the voltage range so as to avoid such a region.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0037]

As described above, according to the present invention, the following effects can be obtained.

(1) According to the first aspect of the present invention, LS
The dependency of the feedback resistance of the oscillation circuit incorporated in I on the power supply voltage can be reduced, and the feedback resistance can be stabilized.

(2) According to the second aspect of the present invention, it is possible to suppress the fluctuation of the feedback resistance value due to the power supply voltage in any voltage range.

(3) According to the third or fourth aspect of the present invention, a feedback resistance value can be obtained with a simple circuit configuration.

[Brief description of the drawings]

FIG. 1 is a feedback resistor circuit diagram in an oscillation circuit according to a first embodiment of the present invention.

FIG. 2 is a feedback resistor circuit diagram in an oscillation circuit showing a second embodiment of the present invention.

FIG. 3 is a feedback resistor circuit diagram in an oscillation circuit showing a third embodiment of the present invention.

FIG. 4 is an oscillation circuit diagram for a conventional ceramic oscillator.

FIG. 5 is an oscillation circuit diagram for a conventional ceramic oscillator formed as an LSI.

FIG. 6 is a diagram for explaining a problem of a feedback resistor circuit of a conventional oscillation circuit for a ceramic oscillator formed into an LSI.

[Explanation of symbols]

1, 21, 31 Input terminal (XT terminal) 2, 22, 32 Inverted output terminal (XT inverted terminal) 3, 23, 33 First inverter 4, 24, 34 Second inverter 5 Analog switch (analog SW) 6 , 25 N-type transistor NTr (NMOS) 7, 13, 27, 40 Resistance element 8, 28 N-type transistor NTr which is always on
(NMOS) 9, 14, 29, 39, 41 Ground (G) 11, 35 P-type transistor PTr (PMOS) 12, 37 P-type transistor PTr which is always on
(PMOS) 26 Gate electrode of N-type transistor NTr 36, 38 Gate electrode of P-type transistor PTr

Claims (4)

[Claims] In a feedback resistor in an oscillation circuit, a feedback resistor of the oscillation circuit is constituted by a transistor, and a gate electrode of the transistor is supplied with a voltage divided by a transistor and a resistance element which are always on. A feedback resistor in an oscillation circuit, characterized in that: 2. The feedback resistor according to claim 1, wherein the transistor is a P-type transistor and an N-type transistor.
A P-type transistor and an N-type transistor.
A feedback resistor in an oscillation circuit, wherein a voltage divided by a transistor which is always on and a resistive element is applied to a gate electrode of the type transistor. 3. The feedback resistor in the oscillation circuit according to claim 1, wherein a voltage divided by an N-type transistor and a resistance element is applied to the transistor. 4. The feedback resistor in the oscillation circuit according to claim 1, wherein a voltage divided by a P-type transistor and a resistance element is applied to the transistor.