Circuit arrangement for generating a signal having a specific waveform with an adjustable voltage level

This is a continuation of International Application Ser. No. PCT/EP00/10990, with an international filing date of Nov. 7, 2000, published in German under PCT Article 21(2).

The present invention relates to a circuit arrangement for generating specific waveforms, in particular waveforms which can be used for generating sound in (mobile) telephones.

In order to generate sound in telephones, it is necessary to produce a signal with any waveform and an adjustable voltage level (amplitude). The signal generated in this manner can then be transformed into sound waves with the aid of capacitive sound transducers, for example.

For multi-tone calling, in particular, such as used in modern telephony, it is necessary to provide a circuit arrangement that can generate the signal described above in the desired waveform. Known circuit arrangements use a relatively high constant supply voltage for this purpose in order to derive the desired signal with the aid of an appropriate voltage transformer.

According to an aspect, a circuit arrangement is provided for generating waveforms, the arrangement having a voltage transformer circuit for generating an output signal with a specific waveform. The arrangement includes a control circuit that is configured to activate the voltage transformer circuit, wherein the control circuit generates a first control signal and a second control signal to activate the voltage transformer circuit. The voltage transformer circuit is configured so that a voltage of the output signal is increased by application of the first control signal and reduced by application of the second control signal.

FIG. 1 is a schematic block diagram of a circuit arrangement for generating waveforms according to the present disclosure.

FIG. 2 illustrates a circuit design for the voltage transformer illustrated in FIG. 1 .

FIGS. 3A and 3B are signal curves illustrating how the circuit arrangement illustrated in FIG. 1 operates.

The circuit arrangement illustrated in FIG. 1 , which may be used in mobile telephones for multi-tone calling, has a DC/DC voltage transformer 4 , which may be in the form of a DC/DC up-controller with voltage reduction capability. The voltage transformer 4 is therefore in a position to both increase and decrease its output voltage V OUT .

The voltage transformer 4 , which modulates the waveform of its output signal V OUT , is activated via two control signals V H and V L , the output voltage V OUT being increased by means of the control signal V H and reduced by means of the control signal V L . Every control signal V H or V L is generated by a corresponding pulse width modulation unit (PWM unit) 2 or 3 , which modulates the frequency and/or pulse width of the respective pulse-shaped control signals depending on modulation signals which are pre-set from a control unit 1 . The PWM unit 2 and 3 , along with the control unit 1 , collectively comprise a control circuit.

The control unit 1 receives a reference signal V REF , which it compares with the actual value of the output signal V OUT . Depending on the result of the comparison, pulse width modulation signals pwm 1 and pwm 2 for modulating the pulse width and/or frequency modulation signals f 1 and f 2 for modulating the frequency of the control signals V H and V L are generated. The pulse width modulation and frequency modulation signals are pre-set for PWM unit 2 and PWM unit 3 , enabling the PWM units 2 and 3 to produce the control signals V H and V L depending on the respective pre-set modulation values. Accordingly, the pulse width and/or the frequency of the pulse-shaped control signals V H and V L is controlled or adjusted depending on the reference signal V REF in such a way that the desired waveform occurs at the output of the voltage transformer, the output voltage V OUT being increased by pulses at the input of the voltage transformer 4 assigned to the control signal V H and reduced by pulses at the input assigned to the control signal V L . Thus, the circuit arrangement illustrated in FIG. 1 corresponds in principle to a delta-modulated DC/DC transformer.

FIG. 2 illustrates one possible configuration of the voltage transformer 4 , in which the voltage transformer 4 is set up as a circuit operating on a supply voltage V 0 and comprises two bipolar transistors T 1 , T 2 , a coil L, a diode D, a capacitor C and resistors R 1 –R 3 . As shown, the transistor T 1 and coil L are connected in series. The diode D and capacitor C are also connected in series, this series connection being in parallel with transistor T 1 . Furthermore, the transistor T 2 is shown connected in series with resistor R 3 , this series connection being in parallel with the capacitor C. Also, the emitters of the transistors T 1 and T 2 are connected together.

As illustrated in FIG. 2 , the individual components are connected so that the control signal V H is applied via the terminal resistor R 1 to the base terminal of the bipolar transistor T 1 and the control signal V L via the terminal resistor R 2 to the base terminal of the bipolar transistor T 2 . The output voltage V OUT maybe tapped from the capacitor C, as shown. As mentioned above, the output voltage V OUT is increased by V H pulses at the bipolar transistor T 1 and decreased by V L pulses at the bipolar transistor T 2 .

Either the pulse width or the frequency or alternatively both the pulse width and the frequency of the two control signals V H and V L may be modulated by the control unit 1 , the circuit arrangement illustrated in FIG. 1 being guaranteed to function in each of these situations.

To illustrate the simplicity of the system, an example of an embodiment will be described below, in which the two PWM units 2 and 3 are operated at a constant frequency and only the pulse width of the two control signals V H and V L is modulated by the control unit 1 and PWM units 2 and 3 . This being the case, the pulse width may be digitally modulated using counters, which are operated at a higher clock rate. The frequency of the two PWM units 2 and 3 may be 128 kHz, for example, while the counter rate is 10.368 MHz, which means that there are 81 different pulse widths for the two control signals V H and V L .

The control unit 1 operates digitally and determines the pulse width to be modulated by the two PWM units 2 and 3 from the differential signal e(k) of the reference signal x(k) and the output signal y(k), i.e., e(k)=x(k)−y(k), where k respectively denotes the sampling time. The control unit 1 defines the value of the pulse width PW depending on the differential signal e(k) as follows:

If e ( k )>0: PW= √{square root over (2· C·L (2 ·e ( k )· y ( k )+ e ( k )· e ( k )))}{square root over (2· C·L (2 ·e ( k )· y ( k )+ e ( k )· e ( k )))}{square root over (2· C·L (2 ·e ( k )· y ( k )+ e ( k )· e ( k )))}{square root over (2· C·L (2 ·e ( k )· y ( k )+ e ( k )· e ( k )))}/( T·V 0 )

If e ( k )<0: PW=−R·C· 1 n ( y ( k )/( y ( k )+ e ( k ))/ T

where C denotes the value of the capacitor illustrated in FIG. 2 , L the inductance value of the coil, R the value of the resistor R 3 illustrated in FIG. 2 , 1/T the frequency of the PWM units 2 and 3 and the two control signals V H and V L , and V 0 is the value of the supply voltage illustrated in FIG. 2 . In order to reduce complexity, the above values for the pulse width PW may be determined on an approximate basis, such as by means of a polynomial approximation, for example.

FIGS. 3A and 3B illustrate different signal curves for the circuit arrangement illustrated in FIG. 1 for various discrete sampling times k where C=30nF, L=47μH, R=330Ω, V 0 =2.65V and T= 1/128 kHz. The signal curve (a) given in FIG. 3A corresponds to the reference signal V REF and the signal curve (b) corresponds to the signal pwm 1 or pwm 2 , while the signal curve (c) in FIG. 3B corresponds to the output signal V OUT and the signal curve (d) corresponds to the control voltages V H /V L where V H =“1” and V L =“0”.

The complexity of the circuit can be reduced if the two control signals V H and V L are generated without feedback, i.e., without evaluating the output voltage V OUT of the voltage transformer 4 . This being the case, there is no closed loop control but merely open-loop control, wherein the control unit 1 determines the value of the pulse width PW depending on the reference signal x(k) at constant frequency of the PWM units 2 and 3 as follows:

F ⁢ ⁢ o ⁢ ⁢ r ⁢ ⁢ x ⁡ ( k ) > x ⁡ ( k - 1 ) ⁢ : ⁢ ⁢ P ⁢ ⁢ W = - L R E ⁢ ⁢ C · T · ln ⁡ ( 1 - R E ⁢ ⁢ C V 0 · C L ⁢ ( x 2 ⁡ ( k ) = x 2 ⁡ ( k - 1 ) ) ) F ⁢ ⁢ o ⁢ ⁢ r ⁢ ⁢ x ⁡ ( k ) < x ⁡ ( k - 1 ) ⁢ : ⁢ ⁢ P ⁢ ⁢ W = - R · C T · ( ln ⁡ ( x ⁡ ( k - 1 ) - ln ⁡ ( x ⁡ ( k ) ) )

where R EC in the above formulas denotes the emitter-collector resistance of the bipolar transistor T 1 .

The present disclosed circuit arrangement is therefore useful for generating waveforms using relatively simple means and is highly reliable and accurate. To achieve this, a voltage transformer circuit is used, to which a first and a second control signal is applied. The voltage transformer circuit is provided with the capability of both increasing voltage and reducing voltage, the first control signal being used to increase and the second control signal being used to decrease the output voltage of the voltage transformer circuit. The voltage transformer circuit is activated by modulating the frequency and/or pulse width of the two control signals, the frequency and/or the pulse width of the control signals being regulated or modulated, depending on a reference signal, so that the desired waveform is applied to the output of the voltage transformer circuit.

Moreover, the described circuit arrangement may be configured both as an open loop control without feedback of the output voltage of the voltage transformer circuit or as a closed loop control with feedback of the output voltage of the voltage transformer circuit. The first option reduces the complexity of the circuit whilst the second enables a more accurate output signal of the voltage transformer circuit to be produced.

Although certain apparatus constructed in accordance with the teachings of the invention have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all embodiments of the teachings of the invention fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.