JPH04131048U - drive circuit - Google Patents

Abstract

(57) [Summary] [Objective] To provide a drive circuit with less deterioration of analog output signals. [Structure] By inserting a buffer amplifier between the D/A converter output circuit and the analog output stage circuit, it is possible to separate digital/analog and improve time axis accuracy, producing a high-quality analog output signal with little influence of noise. It has gained.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This idea improves the drive circuit, especially the output stage configuration of the D/A converter. The present invention relates to a drive circuit.

0002

[Conventional technology]

For example, in a CD player, etc., a disc is played back via a pickup. In order to convert the EFM modulated digital signal into an analog signal, a D/A converter is required. The circuit shown in Figure 2 is used as its output drive stage circuit. I'm tired. In FIG. 2, the positive phase and negative phase components that are the output stage of the 1-bit D/A converter 1 are shown. The output currents from the drive stage circuits 1A and 1B are respectively connected to resistor R5 and A low-pass filter consisting of a capacitor C2, a resistor R6, and a capacitor C2 generates low frequencies. is extracted and supplied to operational amplifiers 2A and 2B. Opamp 2A and 2 The output of B is supplied to the non-inverting input terminal and the inverting input terminal of operational amplifier 3, respectively. , the differential component is obtained as an audio analog signal. These positive phase components and negative phase components An analog signal with low distortion and improved S/N ratio can be obtained by differentially combining the components. It will be.

0003

[Problem that the idea aims to solve]

As mentioned above, the conventional drive circuit is based on the drive stage circuit of the D/A converter. Extracts low-frequency components from the output signal using a low-pass filter consisting of a resistor and capacitor. Then, an analog signal is extracted via an operational amplifier. However, since the D/A converter has a highly integrated configuration, its output driver Since the live stage cannot be constructed with large current type chips, it must be received with high impedance. It is sensitive to noise and degrades the output analog signal. Also , the output circuit has an analog circuit configuration, and the D/A converter itself is a high-density digital Since it is a dual circuit, mutual interference between the two circuits is likely to occur, and the output analog signal There is a problem that deterioration of the number occurs.

0004 Therefore, the purpose of this invention was to create a drive circuit with less deterioration of the output analog signal. It is about providing.

[0005]

[Means to solve the problem]

In order to solve the above-mentioned problem, the drive circuit according to this invention is The output signal from the D/A converter is filtered with a low-pass filter. In a drive circuit that outputs analog signals, a high impedance buffer between the D/A converter and the low pass filter; It is configured by inserting and connecting an amplifier.

[0006]

[Effect]

This idea uses a buffer between the D/A converter output circuit and the analog output stage circuit. By inserting an amplifier, digital/analog separation and time axis accuracy can be improved. high-quality analog output signal with little influence of noise.

[0007]

【Example】

Next, this invention will be explained with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a drive circuit according to this invention. The D/A converter 1 is a general-purpose 1-bit D/A converter, and the drive stage The output currents from circuits 1A and 1B are connected to resistors R1 and R2 and buffer amplifier 4. The resistor R3 and capacitor C1 and A low-pass filter consisting of resistor R4 and capacitor C1 extracts the low frequency components. and is supplied to operational amplifiers 2A and 2B. The outputs of operational amplifiers 2A and 2B are The operational amplifier 3 extracts the differential component and outputs it as an analog signal. The buffer amplifiers 4A and 4B are, for example, 5V operating C-MOS, TTL, FE. T-complementary discrete buffer, etc., has sufficient current supply capacity. A high slew rate is desirable.

[0008] In the configuration of Figure 1, the load of D/A converter 1 is a high impedance buffer. Since the frequency amplifier is 4, the D/A converter output is different from the conventional circuit shown in Figure 2. The load on the D/A converter is small, and there is little impact on the inside of the D/A converter. In other words, the times in Figure 1 The output current I1 from the D/A converter 1 in the circuit of FIG. It can be made smaller than the output current I3 from 1. Moreover, if the current supply capacity of the buffer amplifier 4 is sufficient, the circuit of FIG. The impedance consisting of resistors R3, R4 and capacitor C1 is the resistance of the circuit in Figure 2. It can be made smaller than the impedance consisting of R5, R6, and capacitor C2, reducing noise. The impact of this can also be reduced. The power supply VDD2 of the buffer amplifier 4 is connected to the D/A converter 1. It can be driven with a power supply separate from the power supply VDD1 of the buffer amplifier, and the output current is also the same as that of the buffer amplifier itself. The design can be changed in any way and has a high degree of freedom. Additionally, circuit components such as resistors It is easier to change the setting values of R3, R4, and capacitor C1, increasing the degree of freedom. Therefore, it is also possible to improve the sound quality corresponding to the output analog signal. Furthermore, the accuracy of the square wave in the time axis direction is important for the output of a 1-bit D/A converter. As the current supply capacity improves, the square wave rise and fall characteristics improve. be done.

[0009]

[Effect of the idea]

As explained above, the drive circuit according to this invention combines a D/A converter and an adapter. A buffer amplifier is inserted between the analog output stage circuits, so digital/analog Separation is possible, time axis accuracy is high, noise influence is reduced, and high quality analog output signal is obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of a drive circuit according to the invention.

FIG. 2 is a conventional drive circuit diagram.

[Explanation of symbols]

1 D/A converter 1A, 1B
Drive stage circuit 2A, 2B, 3 Operational amplifier 4, 4A, 4B Buffer amplifier

Claims (1)

[Scope of utility model registration request] In a drive circuit that filters an output signal from a D/A converter with a low-pass filter and outputs an analog signal, a high-impedance buffer amplifier is inserted and connected between the D/A converter and the low-pass filter. drive circuit.