JP3216594B2 - System LSI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillator
The present invention relates to a system LSI having a bit DA converter, a block for processing a crystal oscillation clock from the crystal oscillation circuit, and a selector circuit.

[0002]

2. Description of the Related Art Conventionally, a 1-bit DA converter is connected to a system L.
When trying to obtain good analog characteristics by mounting on an SI, it was necessary to pay attention to the following points.

(1) As a clock input to a 1-bit DA converter, a clock having little noise and jitter is used.

(2) The power supply of the PWM modulation circuit of the 1-bit DA converter and the power supply of the inverter connected to the PWM modulation circuit have low noise.

To realize these contents, one bit D
When the A converter is mounted on the system LSI, the power supply of the crystal oscillation circuit, the power supply of the 1-bit D / A converter, and the power supply of the other logic circuits are configured to be electrically independent of each other.

FIG. 2 shows a 1-bit DA converter using a system LS.
1 shows a configuration diagram of power supply when mounted on an I. FIG.

In FIG. 2, reference numeral 21 denotes a crystal oscillation circuit;
Is a 1-bit DA converter, 23 is a 1-bit DA converter 22
And 24, a crystal oscillation clock output from the crystal oscillation circuit 21, CVDD, CVSS, AVD
D, AVSS, DVDD, and DVSS represent a power supply terminal and a ground terminal that supply a power supply potential and a ground potential to each block of the crystal oscillation circuit 21, the 1-bit D / A converter 22, and the logic circuit 23 other than the 1-bit D / A converter, respectively. .

The 1-bit DA converter 22 is connected to a system LSI
If it is only mounted on a 1-bit D
The analog characteristic of the A converter 22 is a 1-bit DA converter 22
Closed to the characteristics of a single unit.

However, recently, a 1-bit D / A converter not only receives a crystal oscillation clock from a crystal oscillation circuit but also has a block for processing the crystal oscillation clock from the crystal oscillation circuit. A configuration in which a clock signal output from a block for processing an oscillation clock and a crystal oscillation clock from a crystal oscillation circuit are input to a selector circuit, and an output signal from the selector circuit is input to a 1-bit DA converter. System LSI
Is increasing.

Examples of a block for processing a crystal oscillation clock from a crystal oscillation circuit include a VCO, a phase comparator,
It is composed of a circuit such as a frequency divider, and the crystal oscillation clock 24 from the crystal oscillation circuit is
There is a circuit that obtains a clock having a frequency different to the extent.

[0011] Such a clock is used for karaoke and the like, and is used when music is reproduced from the original music tempo. For such an application, generally, the quality of a clock passing through a block for processing a crystal oscillation clock from a crystal oscillation circuit is determined when the crystal oscillation clock from the crystal oscillation circuit is directly used as a 1-bit D / A converter clock. Several dB compared to clock quality
To several tens of dB is often permissible.

Such a system LSI has two or more audio reproduction modes. In the basic mode, the crystal oscillation clock from the crystal oscillation circuit is directly used as a 1-bit DAC clock through the selector circuit.
In this case, since it is used for playing music on a CD,
A high quality clock with little noise and jitter is required.

In the application mode, the crystal oscillation clock from the crystal oscillation circuit is input to the block for processing the crystal oscillation clock, the output from the block for processing the crystal oscillation clock is input to the selector circuit, and the output from the selector circuit is output. The signal is used as a 1-bit DA clock. In this case, since it is used for reproducing music for karaoke, a high-quality clock is not often required.

FIG. 3 shows a conventional system L in such a case.
1 shows a configuration diagram of a power supply of SI. In FIG. 3, 31 is a crystal oscillation circuit, 32 is a 1-bit D / A converter, 33 is a logic circuit other than the 1-bit D / A converter 32, 34 is a crystal oscillation clock output from the crystal oscillation circuit 31, and 35 is the crystal oscillation clock. A block for processing the crystal oscillation clock from the circuit, 36 is a selector circuit, 37 is a crystal oscillation circuit 31
A clock signal which is an output from a block for processing the crystal oscillation clock 34 from the CPU, 38 is an output signal of the selector circuit 36, CVDD, CVSS, AVDD, AVSS,
DVDD and DVSS each include a crystal oscillation circuit 31, a 1-bit D / A converter 32, and a logic circuit 33 other than the 1-bit D / A converter (including a block 35 for processing a crystal oscillation clock from the crystal oscillation circuit 31 and a selector circuit 36).
1 shows a power supply terminal and a ground terminal for supplying a power supply potential and a ground potential to each block.

In FIG. 3, a crystal oscillation clock 34 output from a crystal oscillation circuit 31 is input to a logic circuit 33 other than the 1-bit DA converter. The crystal oscillation circuit 31 is provided inside the logic circuit 33 other than the 1-bit DA converter 32.
There is a block 35 for processing the crystal oscillation clock 34 from the crystal oscillator 34. The crystal oscillation clock 34 output from the crystal oscillation circuit 31 is also input to the block 35 and the frequency and the like are processed. Crystal oscillation clock 3 from crystal oscillation circuit 31
4 is input to a first input terminal of a selector circuit 36, and a signal 37 from a block 35 for processing a crystal oscillation clock 34 from the crystal oscillation circuit 31 is input to a second input terminal of the selector circuit 36. An output signal 38 is input to the 1-bit DA converter 32.

A block 35 for processing the crystal oscillation clock 34 from the crystal oscillation circuit 31 and a selector circuit 36 exist inside the logic circuit 33 other than the 1-bit DA converter 32. The power supply potential and the ground potential are D, respectively.
Power is supplied from a power terminal and a ground terminal represented by VDD and DVSS.

With this configuration, the 1-bit DA converter 32
In a mode in which the crystal oscillation clock 34 from the crystal oscillation circuit 31 is directly used, the power supply of the selector circuit 36 is set to be the same as the power supply of the block 35 for processing the crystal oscillation clock 34 from the crystal oscillation circuit 31. Therefore, the output signal 38 of the selector circuit 36 is configured to be affected by the power supply potential (DVDD) of the logic portion having much noise. As mentioned earlier, when the 1-bit D / A converter 32 is mounted on a system LSI, it is necessary to pay attention to the fact that the clock input to the 1-bit D / A converter 32 uses a clock with little noise and jitter. there were.

Since the conventional configuration violates this principle in using a 1-bit D / A converter for a system LSI,
The analog characteristics of the 1-bit DA converter could not be improved.

[0019]

In the system LSI configured as described above, the analog characteristics of the 1-bit D / A converter, particularly, the signal-to-noise ratio (S / N), the total harmonic distortion (THD), etc. There is a drawback that the characteristics are deteriorated by one digit or more compared to the case of a single-bit DA converter alone.

The present invention solves the above-mentioned conventional problems. In addition to the input of the crystal oscillation clock from the crystal oscillation circuit to the 1-bit DA converter, the present invention processes the crystal oscillation clock from the crystal oscillation circuit. A clock signal that is an output from a block that processes a crystal oscillation clock from the crystal oscillation circuit and a crystal oscillation clock from the crystal oscillation circuit are input to a selector circuit, and an output signal from the selector circuit is provided. Is input to the 1-bit D / A converter.
It is an object to provide means for improving the analog characteristics of the 1-bit DA converter.

[0021]

To achieve this object, a system LSI according to the present invention comprises a crystal oscillation circuit, a 1-bit D / A converter, a block for processing a crystal oscillation clock from the crystal oscillation circuit, Either the output of the crystal oscillation circuit or the output of the block is selected and the 1-bit D
A power supply for the crystal oscillation circuit, a power supply for the 1-bit D / A converter, and a power supply for a block for processing a crystal oscillation clock from the crystal oscillation circuit. And the power supply of the selector circuit is configured to be the same power supply as the power supply of the crystal oscillation circuit.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to this configuration, in a mode in which a 1-bit D / A converter directly uses a crystal oscillation clock from a crystal oscillation circuit, a configuration is adopted in which the power supply of the selector circuit is the same as the power supply of the crystal oscillation circuit. Therefore, the output signal of the selector circuit is not affected by the power supply potential (DVDD) of the logic part having much noise. As a result, the analog characteristics of the 1-bit DA converter can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 1A is a configuration diagram of a power supply of a system LSI according to Embodiment 1 of the present invention. FIG. 1 (a)
1, 1 is a crystal oscillation circuit, 2 is a 1-bit D / A converter, 3a is a logic circuit other than the 1-bit D / A converter 2 and the selector circuit 6, 4 is a crystal oscillation clock output from the crystal oscillation circuit 1, and 5 is a crystal. A block for processing the crystal oscillation clock 4 from the oscillation circuit 1, 6 a selector circuit,
Reference numeral 7 denotes a clock signal which is an output from a block for processing the crystal oscillation clock from the crystal oscillation circuit 1, 8 denotes an output signal of the selector circuit 6, CVDD, CVSS, AVDD,
AVSS, DVDD and DVSS are respectively a crystal oscillation circuit 1 and a selector circuit 6, a 1-bit DA converter 2, a 1-bit DA converter and a logic circuit 3a other than the selector circuit.
A power supply terminal and a ground terminal for supplying a power supply potential and a ground potential to each block (including a block 5 for processing the crystal oscillation clock 4 from the crystal oscillation circuit 1) are shown.

In FIG. 1A, the crystal oscillation clock 4 output from the crystal oscillation circuit 1 is supplied to the selector circuits 6 and 1.
It is input to a logic circuit 3 a other than the bit DA converter 2 and the selector circuit 6. A block 5 for processing the crystal oscillation clock 4 from the crystal oscillation circuit 1 exists inside the logic circuit 3a other than the 1-bit DA converter 2 and the selector circuit 6, and the crystal oscillation clock 4 output from the crystal oscillation circuit 1 , Are also input, and processing such as frequency is performed. The crystal oscillation clock 4 from the crystal oscillation circuit 1 is input to a first input terminal of the selector circuit 6, and a clock signal 7, which is an output from a block for processing the crystal oscillation clock 4 from the crystal oscillation circuit 1, is supplied to the selector circuit 6. And the output signal 8 of the selector circuit 6 is set to 1
It is input to the bit DA converter 2.

1-bit DA converter 2 and selector circuit 6
A block 5 for processing the crystal oscillation clock 4 from the crystal oscillation circuit 1 exists inside the logic circuit 3a other than the logic circuit 3a, but the selector circuit 6 exists in the same power supply block as the crystal oscillation circuit 1, The ground potential is supplied from a power supply terminal represented by CVDD and CVSS and a ground terminal, respectively.

In a mode (basic mode) in which the 1-bit DA converter 2 directly uses the crystal oscillation clock 4 from the crystal oscillation circuit 1, the power supply of the selector circuit 6 is set to the same power supply as the power supply of the crystal oscillation circuit 1. To take
The output signal of the selector circuit 6 is no longer affected by the power supply potential (DVDD) of the noisy logic section.

As a result, it is possible to improve the analog characteristics of the 1-bit DA converter 2.

In the first embodiment, reproduction of music for karaoke is assumed as an application of the application mode, so that a high-quality clock is not often required.

However, new applications will be developed in the future,
A high-quality clock may be required as a clock in the application mode. As such an example, there is an embodiment of claim 2.

(Embodiment 2) FIG. 1B is a configuration diagram of power supply of a system LSI according to Embodiment 2 of the present invention. In FIG. 1B, 1 is a crystal oscillation circuit, 2 is a 1-bit D / A converter, and 3b is a block other than the 1-bit D / A converter 2, the selector circuit 6, and the block 5 other than the block 5 that processes the crystal oscillation clock from the crystal oscillation circuit 1. A logic circuit, 4 a crystal oscillation clock output from the crystal oscillation circuit 1, 5 a block for processing the crystal oscillation clock 4 from the crystal oscillation circuit 1,
6 is a selector circuit, 7 is a clock signal which is an output from a block for processing the crystal oscillation clock 4 from the crystal oscillation circuit 1, 8 is an output signal of the selector circuit 6, CVD
D, CVSS, AVDD, AVSS, DVDD, DVS
S, CVDD1 and CVSS1 are crystal oscillation circuits 1 respectively.
A logic circuit 3b other than the block 5 for processing the crystal oscillation clock 4 from the 1-bit D / A converter 2, the 1-bit D / A converter 2, the selector circuit 6 and the crystal oscillation circuit 1; A power supply terminal and a ground terminal for supplying a power supply potential and a ground potential to each block of the block 5 for processing the crystal oscillation clock 4 are shown.

In FIG. 1B, the selector circuit 6 exists in the same power supply block as the crystal oscillation circuit 1, and these power supply potentials and ground potentials are CVDD and CVS, respectively.
The power supply potential and the ground potential of the block 5 for processing the crystal oscillation clock 4 from the crystal oscillation circuit 1 as well as the power supply terminal and the ground terminal represented by S are represented as CVDD1 and CVSS1, respectively. Power terminal and ground terminal.

With this configuration, not only can the analog characteristics of the 1-bit DA converter 2 be improved, but also the block 5 for processing the crystal oscillation clock 4 from the crystal oscillation circuit 1 in the application mode. Are no longer affected by the power supply potential (DVDD) of the noisy logic section. This makes it possible to improve the analog characteristics of the 1-bit DA converter 2 not only in the basic mode but also in the application mode.

In the present invention, a 1-bit D / A converter has been described as an example of a D / A converter. However, the invention is not limited to a 1-bit D / A converter.

[0034]

As described above, the present invention has a block for processing the crystal oscillation clock from the crystal oscillation circuit as well as inputting the crystal oscillation clock from the crystal oscillation circuit to the 1-bit DA converter. A clock signal, which is an output from a block for processing a crystal oscillation clock from the crystal oscillation circuit, and a crystal oscillation clock from the crystal oscillation circuit are input to a selector circuit, and an output signal from the selector circuit is the one-bit DA signal. In a system LSI configured to be input to the converter, an effect of improving the analog characteristics of the 1-bit DA converter is provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of power supply of a system LSI according to an embodiment of the present invention;

FIG. 2 is a configuration diagram of power supply when a 1-bit DA converter is mounted on a system LSI;

FIG. 3 is a configuration diagram of power supply of a conventional system LSI.

[Explanation of symbols]

Reference Signs List 1 crystal oscillation circuit 2 1-bit DA converter 3a logic circuit other than 1-bit DA converter and selector circuit 3b logic circuit other than 1-bit DA converter, selector circuit and block for processing crystal oscillation clock from the crystal oscillation circuit 4 Crystal oscillation clock output from crystal oscillation circuit 5 Block for processing crystal oscillation clock from crystal oscillation circuit 6 Selector circuit 7 Clock signal output from block for processing crystal oscillation clock from crystal oscillation circuit 8 Selector circuit Output signal

Claims (2)

(57) [Claims] A crystal oscillator circuit, a 1-bit D / A converter,
A block for processing a crystal oscillation clock from the crystal oscillation circuit, and a selector circuit for selecting either the output of the crystal oscillation circuit or the output of the block and outputting the output to the 1-bit D / A converter. The power supply for the circuit, the power supply for the 1-bit D / A converter, and the power supply for the block that processes the crystal oscillation clock from the crystal oscillation circuit are electrically independent of each other, and the power supply for the selector circuit is A system LSI characterized in that the power supply is the same as the power supply of the crystal oscillation circuit. 2. A power supply of a block for processing a crystal oscillation clock from a crystal oscillation circuit is electrically independent from a power supply of the crystal oscillation circuit, a power supply of the 1-bit D / A converter, and a power supply of other logic units. The system LSI according to claim 1, wherein the system LSI is configured.