JPH0585087B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a compander circuit that reduces noise by compressing and expanding signal waves in a communication path. [Prior Art] Conventionally, this type of compander circuit consists of a rectifier made of bipolar transistors and a variable gain amplifier, and the gain of the variable gain amplifier is controlled by a voltage or current obtained by rectifying an input or output signal wave. The amplitude was compressed and expanded. [Problems to be solved by the invention] The conventional compander circuit described above has a circuit configuration that can be easily realized only with bipolar transistors, so it operates in an analog manner, consumes a large amount of power, and requires miniaturization of the circuit. The problem was that it was also difficult. SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and provide a compander circuit made of a digital circuit that is compact and consumes less power. [Means for Solving the Problems] The compander circuit of the present invention has a configuration that includes a rectifier circuit that rectifies an input signal wave, and an oscillation frequency signal that outputs an oscillation frequency signal corresponding to this voltage using the output voltage of this rectifier circuit as a control voltage. a voltage controlled oscillator; a first switch capacitor filter which receives the input signal wave and whose switch circuit is controlled by a clock having an output frequency of the voltage controlled oscillator; and a first switch capacitor filter which is controlled by a constant frequency; The output of the passive filter is input to the second switch which has the opposite frequency characteristic to that of the first switching filter.
It is characterized by including a switch capacitor filter. [Example] Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a compander circuit according to an embodiment of the present invention. The input signal wave V _IN is rectifier 1
and is input to the prefilter 3. The rectifier 1 outputs a DC voltage V _RE according to the amplitude of the input signal wave V _IN . Voltage controlled oscillator 2 (hereinafter referred to as VCO)
uses this DC voltage V _RE as a control voltage and changes the oscillation frequency _S according to its amplitude. When the switch capacitor filter 4 (hereinafter referred to as SCF) is switched at this oscillation frequency _S , the shearing characteristic of the SCF ₄ changes according to the amplitude of the input signal wave V _IN , and as a result, the input signal wave V The gain when _IN passes through SCF ₄ will change depending on its amplitude. Here, the output voltage of SCF ₄ has a constant slope with respect to the signal wave frequency, so an equalization filter 5 with an opposite slope to that of SCF 4 is inserted after SCF ₄ to make it flat. ) characteristics. In addition, in order to reduce aliasing noise and clock components caused by sampling, a pre-filter 3 and a post-filter 6, which are made up of ordinary RC active filters, are installed at the first and last stages of the signal path. I'm taking out _{the OT} . Circuits 1 to 6 listed above can all be configured with MOS type transistors, and the MOS of the compander circuit
It becomes possible to create integrated circuits. Specific examples of each of these blocks are shown in FIGS. 2 to 5. FIG. 2 is a circuit diagram of an example of the flow rectifier 1 shown in FIG. This circuit consists of an operational amplifier 7, a comparator 8, an inverter 9, and transistors T ₁ , T ₂ ,
Consists of resistors R ₁ to R ₃ and capacitor C ₁ ,
Outputs a DC output voltage V _OT in response to the input signal V _IN . 3a and 3b are circuit diagrams of an example of the voltage controlled oscillator 3 of FIG. 1 and an example of its constant current source. This circuit 3 includes constant current sources 10 and 11, and an operational amplifier 1.
2. It is composed of an inverter 13, transistors T ₃ and T ₄ , resistors R ₄ and R ₅ , and a capacitor C ₂ , and an output of an oscillation frequency _S corresponding to the control voltage V _OT from the output of the rectifier 1 is obtained. In this case, the constant current sources 10 and 11 are connected to the operational amplifier 1 as shown in FIG. 3b.
4. A current I is outputted in response to a control voltage V _C by a circuit including a transistor T ₅ and a resistor R ₆ . FIG. 4 is a circuit diagram of an example of the prefilter 3 and postfilter 6 shown in FIG. 1. This circuit is
It consists of an operational amplifier 15, resistors _R7 , _R8 , and capacitors _C3 , _C4 , and the resistors _R7 , _R8 and capacitors _C3 , _C4 are set to appropriate values to obtain a filter with predetermined characteristics. ing. FIGS. 5a and 5b are circuit diagrams of an example of the SCFs ₄ and ₅ shown in FIG. 1 and a transfer gate used therein. As shown in FIG. 5a, this SCF is composed of four stages of operational amplifiers 16 to 19, transfer gates G1 to 12 and G21 to 32 that switch signals, and capacitors C10 to C22 that are switched by these transfer gates. be done. In addition, transfer gates G1 to G12, G21 to 32 are
As shown in FIG. 5b, it is composed of an N-MOS transistor and a P-MOS transistor, and a clock and its inverted signal are input to the gates of these transistors.
12 and transfer gates G21 to G32 can be switched to either one. Next, the operation of this embodiment will be explained using a specific example. FIG. 6 is a frequency characteristic diagram showing the amplitude expansion operation as a specific example of this embodiment, and these are the following first
The characteristics of states A to C in the table are shown.

[Table] Now, set the input voltage level of the reference signal wave to V _INO
(dB), then the rectified output V _REO (V), VCO3
output frequency _SO (Hz), SCF cut-off frequency _CO
(Hz) and signal wave output voltage level V _OTO (dB)
shall be. In addition, if SCF ₄ is an LPF with a shearing frequency below the signal band and has a slope of -24 dB/COT, its shearing characteristic line will be A in Figure 6.
It will look like this. At this time, the equivalent filter 5 has a cutoff frequency that is above the signal band, and is +24 dB/
HPF with OCT slope is used. If the input wave V _IN is lowered by 10 dB from the reference level (A), the characteristic line B will appear. As a characteristic of VCO3, the input wave V _IN is α (dB) below the reference level.
Assuming that the oscillation frequency becomes 2 ^- 〓 ^/24 times as it decreases, the output frequency _S becomes 2 ^-10/24 _SO . Generally, in SCF, the cutting frequency _C is the oscillation frequency
Since it is proportional to _S , the shear frequency _C is 2-1
0/24・_CO , and its shear characteristic line is like B in Figure 6, which is uniform in the signal wave band.
10dB down. Therefore, the output wave V _OT is V _OTO −20 (dB)
becomes. Furthermore, if the input wave V _IN is lowered by 10 (dB),
Oscillation frequency = _S becomes 2 ^-20/24・_SO , and the shearing frequency _C also becomes 2 ^−20/24・_CO , so the shearing characteristic line becomes like C in Figure 6, and the signal wave The band is further uniformly lowered by 10dB. Therefore, the output wave V _OT is V _OTO
-40 (dB). Looking at the relationship between the input wave V _IN and the output wave V _OT from the above, we can see that the level difference from the reference voltage at the input of the signal wave is twice the decibel value at the output, and the amplitude is expanded. It can be seen that the action is taking place. Furthermore, the dynamic range of the input wave V _IN is determined by the characteristics of the VCO and the characteristics of the SCF, but in this example, the frequency variable range of the VCO is set to 0.1 _SO
~ _SO , the dynamic range of the input wave V _IN will be approximately 80 dB. FIG. 7 is a frequency characteristic diagram showing the amplitude compression operation as another specific example of this embodiment.
These show the characteristics of states D to F in Table 2 below. Now, set the input voltage level of the reference signal wave to V _IN2
(dB), and the values of V _RE , _S , _C and V _OT at that time are V _RE2 , 〓 _S2 , _C2 and V _OT2 . Also, SCF ₄
Assuming that has a slope of +12 dB/OCT at HPF, the shear characteristic line will look like E in Figure 7.

〔Effect of the invention〕

As explained above, the present invention constructs a compantor circuit using a rectifier made of MOS transistors, a voltage controlled oscillator, an active filter, and a switched capacitor filter.
A compander circuit that can be made into a small MOS integrated circuit with low power consumption can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a compander circuit according to an embodiment of the present invention, FIGS. 2, 3, 4, and 5.
The figure is a circuit diagram showing specific examples of the rectifier circuit, voltage controlled oscillator, pre- and post-filter, and switch capacitor filter shown in Figure 1. Figures 6 and 7 are amplitude expansion and compression operations of this embodiment. FIG. 1... Rectifier, 2... Voltage controlled oscillator (VCO), 3... Prefilter, 4... Switch capacitor filter (SCF), 5... Equivalent filter, 6... Post filter, 7, 12, 14
~19... operational amplifier, 8... comparator,
9, 13... Inverter, 10, 11... Constant current source, C1-C3, C10-C22... Capacitor, G1-12, G21-32... Transfer gate, T1-T5... MOS transistor, R
1 to R8...Resistance.

Claims (1)

[Claims] 1. A rectifier circuit that rectifies an input signal wave, and a voltage controlled oscillator that uses the output voltage of this rectifier circuit as a control voltage and outputs an oscillation frequency signal corresponding to this voltage.
a first switch capacitor filter which receives the input signal wave and whose switch circuit is controlled by a clock having an output frequency of the voltage controlled oscillator;
A compander comprising a second switch capacitor filter that is controlled by a constant frequency, receives the output of the first switch capacitor filter, and has a frequency characteristic opposite to that of the first switch capacitor filter. circuit.