TDA3810 surround sound processor. Reference data

Encyclopedia of radio electronics and electrical engineering / Application of microcircuits

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The TDA3810 chip is designed to work in the AF channels of radio and television receivers, as well as in other sound-reproducing equipment. It provides three modes - "Stereo", "Extended stereo" and "Pseudo stereo". In the first one, both channels of the processor have a unity gain, i.e. they work as voltage followers. In the second, a signal from the neighboring channel is added in antiphase to each channel, which subjectively expands the stereo base. The third mode is designed to convert a monophonic signal into a pseudostereo one.

The microcircuit is framed in an 18-pin plastic SOT 102 package (Fig. 1).

Fig. 1

A simplified functional diagram of the processor [1] is shown in fig. 2. Each channel contains an input buffer amplifier with a gain of 1 (DA1 - for the left channel, top in the diagram), three amplifiers (DA2-DA4), the outputs of which are switched by an electronic switch (S1.1), and an output buffer amplifier (DA5). The operating point of the amplifiers is set by the voltage divider R7R8, and the signal divider R3R4 determines the gain of the op amp DA3 in the "Extended stereo" mode.

Fig. 2

The signals for switching the outputs of amplifiers DA2-DA4 are generated by the control device. It contains an input logical node and an indicator control node.

The microcircuit also includes a device that allows you to turn on the processor gently, without clicking in acoustic devices. It works if a large capacitor is connected between terminal 9 and the common wire.

Pinout of the microcircuit: pin. 1-output of a resistive voltage divider, filter capacitor connection point; pin. 2-left channel input (LIN); pin. 3-output of the input buffer amplifier of the left channel (LAMP); pin. 4-OS signal input for the "Extended stereo" mode on the left channel (LSPAT); pin. 5-input of the amplifier - the shaper of the pseudo-stereo effect of the left channel (LPSD); pin. 6-left channel output (LOUT); pin. 7-pin for connecting an LED that induces the inclusion of "Extended stereo"; pin. 8-pin for connecting an LED that induces the inclusion of the "Pseudo-stereo" mode; pin. 9-pin for connecting the capacitor of the "soft" switching device (SSC); pin. 10-common and negative power output; pin. 11 and 12 - control inputs for selecting the operating mode (CNTR1 CNTR2, respectively); pin. 13-right channel output (ROUT); pin. 14-input of the amplifier - the shaper of the pseudo-stereo effect of the right channel (RPSD); pin. 15-OS signal input for the "Extended stereo" mode on the right channel (RSPAT); pin. 16-output right channel input buffer amplifier (RAMP); pin. 17-input of the right channel (RIN); vyv.18-positive power output.

On fig. 3 shows a typical circuit for switching on the microcircuit [2]. Here, capacitors C6, C7, C10 and C13 are separating, C11 is a filter for a supply voltage of 6 V; capacitor C12 is included in the "soft" inclusion system. The role of the remaining elements is explained below when considering specific modes of processor operation.

Fig. 3

Main Specifications

Operating limits

The processor operation mode is selected by applying high and low level signals to the control inputs CNTR1 and CNTR2 (pins 11 and 12) in certain combinations in accordance with the table. These signals can be fed both from standard TTL microchip outputs and from open-collector outputs, for which the necessary load resistors are included in the TDA3810 processor. It is also possible to supply control signals from the outputs of CMOS microcircuits, if they are supplied with a voltage of 2 ... 5,5 V. You can also control the processor using a mechanical switch by connecting pins 11 and 12 of the microcircuit to a common wire.

Table 1

On fig. 4 shows a block diagram of the TDA3810 processor operating in the "Stereo" mode. The transmission coefficient of both channels in this case is equal to 1.

Fig. 4

The functional diagram shown in fig. 5 corresponds to the "Extended stereo" mode. The transfer coefficient from the input of the left channel to its output is 0,66 (1 + R8 / R9), where 0,66 is the transfer coefficient of the internal resistive divider of the processor connected to the non-inverting input of the op-amp DA3, and R8 and R9 are the resistance of external resistors R8 and R9 included in the input filter circuit.

Fig. 5

When indicated in Fig. 3 ratings of these resistors, the transfer coefficient is 1,32 (2,4 dB). The transfer coefficient from the input of the left channel to the output of the right one is negative and equals -0,66R10/R9=-0,66. At the higher frequency components of the audio signal, where the capacitance of the capacitors C8 and C9 is much less than the resistance of the external resistors R8 and R10, the signals at the outputs of the channels repeat the signals from their inputs with a coefficient of 0,66. The conditional frequency separation boundary, below which the stereo base expands, but not above, can be considered the value 1/2πR8C8=4 kHz. If capacitors C8 and C9 are not installed, the stereo base will expand throughout the entire audio frequency band.

Since the channels are built in a similar way, these coefficients are also valid for the right channel.

The scheme in fig. 6 is valid for the "Pseudo-stereo" mode. Here, the same mono signal is fed to both inputs of the stereo processor. The transmission coefficient from the input of the left channel to its output does not depend on frequencies and is equal to -R12/R13=-1,33. The frequency response of the gain from the common mono signal input to the right channel output is determined by the characteristics of the filters Z1 and Z2. Through the filter Z1, assembled on resistors R1-R5 and capacitors C1-C3 (see Fig. 3), a direct input signal is supplied to the inverting input of the processor op-amp DA9. Through the filter Z2-elements R6, R7, C4 and C5, an inverted and amplified signal is fed to the same input from the output of the left channel.

Fig. 6

In addition, the transfer coefficient depends on the resistance of the feedback resistor R11. In order for the transmission coefficients for both outputs to be the same at the lowest frequencies, it is necessary that the resistance of the resistor R11 \u100d 1,33 kΩ be 12 times (R13 / R1) more than the total resistance of the filter resistors Z1, i.e. R2 + R3 + R4 + R76 \uXNUMXd XNUMX kOhm, which is what a typical switching circuit provides.

The Z1 filter is a notch filter with an attenuation frequency of about 500 Hz. Z2-band filter, with the same center frequency. Their parameters are calculated so that the amplitude-frequency characteristic of the output of the right channel is almost uniform, and the phase shift between the channels is close to zero at the edges of the audio band. At a frequency of 500 Hz, the output signals of the stereo processor are out of phase, and a shift of 90 degrees. correspond to frequency values ​​of 150 and 200 Hz. This phase response creates an interesting spatial picture of the sound.

Literature

1. Shkritek P. Reference guide to sound circuitry. - M.: Mir, 1991.-448 p.
2. Philips Semiconductors. TDA3810. Spatial, stereo and pseudo-stereo sound circuit. data sheet. January 1985

Publication: cxem.net

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