JPH08265076A - Control circuit for frequency/phase response of signal amplification system - Google Patents

Abstract

PURPOSE: To improve the flexibility of control or optimization while assembled serial structure is kept by providing plural bypass switches which can functionally short-circuit at least one of elements. CONSTITUTION: The phase shift cells of a signal processing assembled serial system are realized in the form of plural integrated resistors r1-rN where the integrated elements (resistor R in special case) of an RC network deciding a center frequency are in series. Integrated bypass switches S1-SN are connected to the partial elements in parallel. In can be controlled by an operator by programming or selection from a control panel. Thus, the cutoff of the respective cells in the cell assembled serial system, namely, the center frequency can individually be optimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to frequencies and frequencies, especially for audio systems, for performing equalization effects such as so-called "surround" effects in stereo systems and / or for producing special effects of audio reproduction. /
Alternatively, the present invention relates to a circuit that controls the phase response of signal amplification.

[0002]

BACKGROUND OF THE INVENTION To compensate for the inherent frequency response of the elements of the system and / or to optimize the frequency and / or phase response of the amplification system and / or for so-called surround stereo audio systems. A complex equalization requirement in an analog signal amplification system to achieve a special effect, such as an effect, results in the need to form multiple circuit blocks to modify the transfer characteristic, the effect of which is constant Specially selected or not selected for effect. Generally, for audio devices of relatively compact size, such as magnetic tapes or compact disc playback devices installed in cars or portable systems, the so-called embedded serial structure (with respect to the signal path) is preferred. This is because the device is less burdened and less distorted in terms of circuit complexity than an equivalent parallel structure. In fact, the parallel structure requires multiple multiplexers along the signal path that tend to introduce a second harmonic distortion, which is especially harmful in audio systems.

On the other hand, the need to limit the number of elements external to the integrated circuit and at the same time reduce the size of the integrated circuit itself favors the use of embedded serial structures, where the signal being processed is processed. Can be selected and derived from any point in the circuit block chain of equalization / modification cells of the frequency and / or phase response characteristics of the amplification system. Depending on the type of effect produced by the built-in serial correction structure, the structure comprises a series of pure phase shift cells and / or emphasis (amplification) or de-emphasis (attenuation) cells. An important example of these systems are the circuits used to create the so-called "surround" effect of stereo audio systems. In this case, one of the stereo channels
The audio signal transmitted through the channels undergoes a phase shift at certain frequencies in the audio spectrum according to the selected surround mode. The signal passes through a series of blocks or cells containing phase shift circuits, each having a transfer characteristic that is an intervening cutoff frequency that is generally determined by the RC network. The modulated signal is selected and tapped by the operator from any point in the chain of phase shift cells. Such a system is shown schematically in FIG.

Of course, signal phase shift (or frequency response modification) cells have a special configuration. 2, 3, 4, 5 and 6 show different filters and / or phase shift cells used as needed and / or to produce certain effects in the equalization system. Basically each cell comprises an RC circuit suitable for establishing a frequency and / or phase shift response (ie a transfer function). As shown in FIG. 1, the selection of the “tapping” point of the signal from any of the (built-in) cell chains is a global modification for the corresponding channel or amplified signal in terms of frequency and / or phase response. Or allow the selection of optimized properties.

In the case of an embedded serial circuit suitable for producing the "surround" effect of a stereo audio system, each phase shift cell is constructed as a circuit as shown in FIG. On the other hand, in audio systems,
The frequency is that of the so-called audio band (i.e. the low frequency spectrum), so such frequency and / or phase response modification circuits generally require the use of large capacitors external to the integrated circuit or have special capacitances. An amplifier circuit is integrated to limit the number of external devices. In generally known systems, each cell is designed to produce an effect, which alone or in combination with the effects produced by other selected cells in the chain, induces a signal for further processing ( By selecting at the points to be tapped, it is possible to achieve an overall effect on the frequency and / or phase response characteristics of the amplifier.

In the case of a built-in serial structure, the total optimization of the chain suppresses the possibility of special optimization of the single cell as a whole, which is different in that the single cell characteristic is enabled by the selector. This is because they must be combinable with each other in order to produce the overall effect selectable between the combinations. Such features of known types of embedded serial systems imply limitations and drawbacks both in terms of performance and reduced flexibility of adjustment.

In integrated systems, the value of the integrated resistor usually defines the choice of the value of one or more external capacitors of the RC network of various cells. Therefore, changing the value of an external connection element (generally a capacitor) of a cell to optimize its characteristics may result in modification of the response characteristics corresponding to various combinations with other cells of the same cell's built-in chain. means. Whenever such limitations of embedded serial systems are unacceptable, the problem is more costly and causes distortion problems, but generally abandoned embedded serial structures (despite their convenience). This can be avoided by using a parallel structure.

[0008]

OBJECT OF THE INVENTION While retaining the embedded serial structure,
Clearly, there is a need and useful circuit for adjusting the frequency and / or phase response characteristics of signal amplification systems with improved tuning or optimization flexibility comparable to that of parallel systems.

[0009]

This object is fully achieved by a circuit formed in accordance with the invention, which circuit comprises substantially at least one element of the RC circuit of each cell of a built-in serial structure, each of which is a partial value. At least one of said elements having
It is characterized in that it is realized in the form of a plurality of elements, which are connected in series with each other and have a partial value of the design value of the element, which are equipped with a plurality of bypass switches capable of functionally short-circuiting each other. The bypass switch configuration is controlled by a dedicated control circuit that is programmable by the operator. This allows each cell to be individually optimized independently of the others. Furthermore, the selection of tapping points of the signals in the embedded serial chain and for certain combinations a very large number determined both by the configuration of these switches of each RC network of cells functionally active along the signal path. The response characteristics of are realized.

The different features and advantages of the system of the present invention will become clearer through the description of several important aspects which follow with reference to the accompanying drawings. FIG. 1 shows a diagram of an embedded serial system for modification / optimization of the frequency and / or phase response characteristics of an amplification system or channel. 2, 3, 4, 5 and 6
Figure 2 shows a circuit suitable for forming a single cell of the signal processing embedded serial system of Figure 1 used depending on the type of effect required. FIG. 7 shows a phase shift cell functionally similar to the cell of FIG. 2 modified according to the invention. FIG. 8 is an amplification or de-emphasis (attenuation) function similar to the cell of FIG. 4, but using an integrated capacitance whose ratio is suitably modified by an operator programmable programmable capacitance multiplier circuit according to the invention. ) Indicates a cell.

The subject of the invention is the frequency of a signal amplification channel or system having an embedded serial structure comprising a plurality of phase-shifting and / or emphasis and / or de-emphasis cells, as shown schematically in FIG. And / or a circuit for controlling the phase response characteristic. Of course, the available selection options may differ from those shown in FIG. 1 by using different selectors or functionally similar selection circuits. It is important to emphasize that the sample electrical circuit shown is purely illustrative and that the circuit is not intended to limit the field of application of the devices and / or processes of the invention to the particular examples. As already mentioned, the embedded serial system for signal processing can use the different types of cells illustrated in FIGS. In the case of a system designed to produce a so-called surround effect during stereophonic playback, the circuit uses a plurality of phase shift cells, for example of the type shown in FIG. This type of cell or circuit is essentially a pass-all filter that can introduce a phase shift into the frequency band centered at a certain frequency f _{0 of the} audio spectrum determined by f ₀ = ½πRC.

Basically, each of the various cells has its own cutoff or intervention center frequency, each frequency being distributed according to the above criteria throughout the audio band. The operator's special selection of the point from which the signal is induced then determines to select a particular surround effect from the multiple selectable effects. The cells shown in Figures 3 and 4 are clearly bi-quadratic (bi
quadratic) cell (that is, a cell having a transfer function comprising quadratic functions of both the numerator and the denominator). These cells have a substantially bell-shaped frequency response (passband)
And is commonly used in audio processors for performing tone control functions and the like.
The transfer functions of the cells of Figures 3 and 4 are substantially similar.

The cell shown in FIG. 5 has a gain which is less than or equal to 1 and a transfer function which shows a passband type frequency response characteristic. This type of cell is commonly used in de-emphasis circuits. The cell of FIG. 6 shows a typical emphasis circuit for high frequency tones (ie having the characteristics of a high pass filter) suitable for producing in-band gains greater than unity. A sample of an embodiment of the invention is shown schematically in FIG. The cell of FIG. 7 is functionally equivalent to the cell of FIG. As described above, this is a pass-all type phase shift circuit (that has a substantially flat frequency response characteristic) that can be used in a circuit for producing the surround effect of the stereophonic playback system. Shows.

According to an aspect of the present invention, each cell (Cell1, Cell2, Cel) of the embedded serial circuit of FIG.
13 ... Celln) has a circuit similar to that shown in FIG. The integrated elements of the RC network (resistor R in a special case) that determine the center frequency f ₀ are a plurality of integrated resistors r1, r2, r3 ...
It is realized in the form of. Each resistor has a partial value referred to as the design value of the resistor R. Integrated bypass switches (S1, S2, S3 ...
SN), which can be controlled by the operator through programming or selection from the control panel. The drive circuit of the bypass switch is not shown in the circuit diagram shown, but can easily be realized in a suitable manner, as will be immediately apparent to the person skilled in the art. This allows the cut-off or center frequency f ₀ of each cell of the cell's embedded serial system (FIG. 1) to be independently optimized, ie to determine the effective value of the resistance R of the RC network of the cell, Bypass switches S1, S2,
S3 ... The state of SN can be changed by setting the operator within a certain range.

The all-embedded serial system shown diagrammatically in FIG. 1 has surprising flexibility. In other words,
A very large number of possible combinations are formed, which are relatively small in deriving the first series of "several" cells,
It is maximal upon induction of the signal after the series of "last" cells (CellN). Given that the circuit of FIG. 1 comprises n cells and each cell (FIG. 7) is implemented with a resistor module of N configurations, the user may have many possible combinations, ΣN.
^It has a number of freely selectable separate effects given by ⁿ (n = 1, m). Of course, resistors r1, r2, r3
It is convenient to integrate the rN bypassable module and the bypass switches S1, S2, S3 and SN. Configuration switches S1, S2, S3
... The SNs can be digitally controlled, so they can be implemented with simple "transfer gates", which do not compromise the system with respect to noise and / or distortion if they have the correct dimensions.

The circuit diagram of FIG. 8 shows a biquadratic circuit having a bypass frequency response characteristic designed to either attenuate or amplify the signal in the band, which is functionally. It is similar to the cell shown in FIG. The capacitance C of the RC network of signals illustrated in FIG. 8 is constituted by an integrated capacitance C _i having a relatively small value, which is preferably doubled by a dedicated integrated capacitance multiplier circuit.
Those skilled in the art will appreciate that the equivalent capacitance produced by a capacitance multiplier is C = C _i ·
(R1 / R2). According to the invention, two voltage dividers R1-R2 of the capacitance multiplier circuit are used.
One of the branches (R1) is realized in the form of a plurality of integrated resistors having partial values r1, r2 and / or r3,
Each resistance module has its own integrated switch S1, S
2. Short circuit is possible through S3.

In this case also, an embedded serial system comprising a plurality of cells having the circuit shown in FIG. 8 (FIG. 1)
Allows "doubling" the number of selectable combinations to obtain the same number of different response characteristics. The invention is particularly useful in systems and devices that must have low cost and high compactness, such as in portable and car playback and radio systems. In these cases, cost, complexity, and size considerations of integrated devices tend to preclude the option of applying parallel structures, and in these circumstances, the present invention reduces the cost, complexity, and complexity of integrated circuits forming audio processors. Allowing to achieve a surprisingly high degree of control flexibility while maintaining sex and size. Removal of external components (generally capacitors) that are commonly sought by manufacturers of electronic devices in the special case of circuits for equalization / modification of response characteristics may result in the device manufacturer implementing certain default conditions. Can be done, for example, by establishing an abbreviated configuration of a plurality of single-cell switches of the embedded serial system, which accounts for the special properties of the other elements of the sound reproduction device. Such customisation, which was generally made possible by choosing the value of the externally connected capacitors, allows one or more selectable omitted configurations of bypass switches of multiple single cells (RC network of cells). Can be more accurately and easily implemented in the system of the present invention by simply limiting

In general, several alternatives are possible.
In particular, a convenient capacitance multiplier circuit, conveniently used to form a plurality of single cell RC networks of a system formed in accordance with the present invention, was filed by the applicant on July 28, 1993. Japanese patent application 5-
No. 207186.

[Brief description of drawings]

FIG. 1 is a diagram of an embedded serial system for modifying / optimizing the frequency and / or phase response characteristics of an amplification system or channel.

FIG. 2 is a circuit showing a first example suitable for forming a single cell of the signal processing embedded serial system of FIG. 1 used depending on the type of effect required.

FIG. 3 is a circuit similarly showing a second example.

FIG. 4 is a circuit similarly showing a third example.

FIG. 5 is a circuit similarly showing a fourth example.

FIG. 6 is a circuit similarly showing a fifth example.

7 is a diagram showing a phase shift cell functionally similar to the cell of FIG. 2 modified according to the present invention.

FIG. 8 is a diagram of a circuit functionally similar to the cell of FIG.

[Explanation of symbols]

r1, r2, r3, rN ... Resistors S1, S2, S
3, SN ... Switch C ... Capacitor

Front page continued (72) Inventor Maurizio Tonera Corvetta 20011 Via Eme Nero 27 Italy

Claims (4)

[Claims] 1. A plurality of emphasis and / or de-emphasis and / or phase shift cells, each having a special RC network capable of determining cascaded response characteristics, and a chain of cascade cells from which signals are derived. 1 from among multiple selectable nodes
In a signal amplification system or a frequency and / or phase response characteristic control circuit for a channel comprising at least one selector capable of selecting one node, at least one element of the RC network of the cell is connected in series. In the form of a series of modules having partial values which are referred to as design values of the device, each further comprising a plurality of bypass switches capable of shorting at least one of said modules of said partial values, and means for setting the state of said switches A circuit further comprising: 2. The signal amplification system is an audio system, the capacitor of the RC network of the cell is a discrete component externally connected to an integrated circuit of the amplification system, and one of the RC network of the cell.
The circuit according to claim 1, wherein the module having partial values of elements, the switch and the setting means are integrated. 3. The circuit according to claim 1, wherein all elements of the RC network of the cell are integrated. 4. The amplification system is an audio system, which comprises an integrated capacitance of at least one capacitor of the RC network of cells and an integrated capacitance multiplier circuit, the multiplication factor of which is provided by a resistive voltage divider. 4. A circuit as claimed in claim 3, in which the established and whose resistance constitutes the element divided in a module, the effective value of which is set by the configuration of the bypass switch.