JPS6059774B2 - step generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a step generator for a companding coater and decoder used in PCM.

In PCM transmission, an analog signal is encoded and transmitted, and on the receiving side, this is encoded and converted into the original analog signal.

The decoder used for this is usually as shown in Figure 1.
It consists of a segment generator SGG and a step generator STG, and the former is composed of a segment 5i (i=1, 2,
...8) An analog voltage A indicating the starting point P is generated, and the latter generates a voltage B divided between the starting point P, the ending point P, and P2 of the segment. In PCM, when encoding, the small amplitude part is enlarged to increase the fidelity, so there is a saturation characteristic (8 segment polygonal line characteristic) between the encoded input signal and the decoded output signal as shown in Figure 3. There is. When the 8-bit input signal DS is input, the control circuit CNT supplies the higher-order bits to the segment generator SGG to generate the starting end potential A of the segment Si in the order determined by the hits, and also outputs the lower-order bits to the segment generator SGG. The divided potential B is applied to a generator STG to generate a divided potential B defined by the plurality of bits.

These are added and the sum becomes the output analog signal AS2. 1. Specifically, as shown in FIG. 2, the segment generator SGG has variable capacitors C, ~C.

The step generation TG is only a variable resistor, R. Consisting of Each of the capacitors C1 to C3 includes a plurality of capacitors and a switch that is opened and closed by a digital input signal DS to insert and remove the capacitors. digital signal D
The switch is opened and closed by S2, and the capacitors Cl and C2
When the value of is changed, the divided potential of the reference voltage Ref is changed, and thus the voltage A is outputted. The variable resistors Rl and R2 consist of a large number of series resistors and a group of switches that are arranged between their series connection point and the output end and are turned on and off by a digital input signal.The switches are turned on and off by an input signal DS2 and used as a reference. Divided voltage B of voltage Vref
This voltage B″ outputs segment order position (1=
1, 2...8) is determined by the lower bit of the signal DS2, but as shown in FIG. 3, the slope of each segment is different, so the required step voltage depends on the segment order. should change accordingly. Capacitor C3 performs this correction. The switch group for insertion and removal of this capacitor C3 is also turned on and off by the upper bit of the input signal DS2, and the capacitance of the capacitor is changed to correct the voltage B'' added to the voltage A to B.A coater used in PCM transmission is the comparator CO as shown in Figure 4.
It consists of MP, successive approximation register SCR, and local decoder DEC.

This local decoder DEC has the same structure as the decoder described above. When an input signal ASl having a value as shown in FIG. 5 is input to the comparator COMP, the decoder DEC initially outputs 0v
Therefore, the comparator generates an H level output, and in response to this, the register SCR outputs 1 of full scale F.
An 8-bit digital signal DSl commanding 12 voltages is output to the decoder DEC. Therefore, the decoder DEC is 0.
The voltage of 5F' is output to the comparator COMP, and the voltage of 0.5
Since F>ASl, the output of the comparator becomes L level. In response to this, the register water * star SCR outputs a digital signal DSl that commands a voltage of 112 of 0.5F'.
The output of the decoder DEC becomes 0.25F. This is AS
Since it is lower than l, the comparator output becomes H level, and in response, the register changes to 0.25F'+0.25F'/2
produces an output that commands the voltage of The same goes for the following, and in this way the decoder output approaches the input analog voltage ASl as much as possible, and the H, L (1.0) of each comparison result between them
represents the digital code of the analog signal ASl, so this is the coded output of the input signal. There are A-law (ALlw) and μ-law (μLiw) for signal companding.

These are, of course, well-known, but to briefly explain A.
According to the rule, the full scale F is 112, as shown in Figure 6a.
114,1 no 8... and segment S8,S
7, S6...S1. Also, according to the μ law, twice the minimum segment S1 is made into segment S2, twice that is made into segment S3, and so on, segment S8 is made in the same manner, and S
1+S2+...S8 becomes full scale F.
Furthermore, the method of dividing one segment is also different between the A-law and the μ-law. In other words, according to rule A, the whole is divided into 32 parts as shown in c in the same figure, and in the case of a coater, 2132, 4132, 6132, etc.
In the case of a decoder, the points of ... are 1132, 313
2,5132... points are each step. μ
In the case of the rule, one segment is divided into three as shown in figure d, and in the case of the coater, the points are 1133, 313 &..., and in the case of the decoder, the points are 0133, 2133, 4133, etc.
Each step is defined as a point. The step generator STG described above outputs each of these step voltages. The above is summarized in Table 1 as follows. By the way, the step generator STG of the coater and decoder has heretofore been made exclusively for the A-law and the μ-law, respectively, and has not been shared. However, although step generators are currently implemented as LSIs, integrated circuits can be mass-produced to reduce costs, so it is preferable to commonly manufacture them as general-purpose products to increase the scale of production. In the step generator for both A-law and μ-law, the maximum number of divisions of one segment is 33 as shown in the table above, so 33 resistors are used, and by connecting them in series and applying a reference voltage, each series connection point is used. If one resistor is removed to make 32 resistors, each step voltage of the A-law can be obtained from each series connection point.

However, in this case, only one step voltage is obtained using three brass resistors, and since there are many resistors, a large area is required, and since there are variations, it is difficult to increase the relative accuracy of each resistance value). There is a problem that it is difficult to increase the yield. Therefore, the present invention attempts to eliminate the above drawbacks by configuring a step generator with as few resistors as possible, about the number of taps.The present invention is characterized by generating an end point potential of a segment. In the step generator of the companding coater, which is composed of a segment generator and a step generator that generates a divided potential between both end points of the segment, an additional resistor on the power supply side with the same resistance value is connected between the power terminal and the ground terminal. and n pieces (n natural numbers)
A series resistor group is connected in series with a ground-side additional resistor having the same resistance value as the power-supply-side additional resistor, and a first mode selector switch is connected in parallel to the power-supply-side additional resistor. Then, another ground-side additional resistor having the same resistance value as the ground-side additional resistor is connected in parallel to the ground-side additional resistor via a second mode selector switch, and is common to each series connection point of the series resistor group. A group of (n+1) output switches that are turned on and off by a digital signal are provided between the output terminal and the first mode changeover switch is turned off and the second mode changeover switch is turned off by a μ law designation signal. The first mode changeover switch is turned on and the second mode changeover switch is turned off by the A-law designation signal.

Next, this will be explained in detail with reference to examples. 7th
The figure shows the connections for the coater of the A/μ compatible step generator according to the invention, and FIG. 8 shows the connections for the decoder of the same generator.

In the case of the coater in FIG. 7 and in the case of the decoder in FIG.
In this embodiment, 15 resistors (indicated by Rn) are connected in series, and in the case of a coater, resistors 10, 12, and 14 with a resistance value R are connected in series, and in the case of a decoder, resistors 10, 12, and 14 with a resistance value R are connected in series. Resistors 10 and 16 and 12 and 14 of value R are connected in series. Therefore, in order to use the resistor as both a coater and a decoder, it is better to use the configuration shown in FIG. 8 as the resistor. Output switches SWl, SW2 . . . SWl6 are connected between each series contact of the 15 series resistors R and the output terminal 20.

In addition, the additional resistors at both ends of this series resistor group include a mode changeover switch S2O that short-circuits the resistor 10 and a mode changeover switch S22 that disconnects the resistor 12 in the case of a coater, and a mode changeover switch S22 that disconnects the resistor 16 in the case of a decoder. switch S2
4 and the above switch S2. and a switch SWO that grounds the output end 20. One end of the additional resistor at both ends of both the coater and decoder is connected to the positive and negative reference voltage sources Vref via a changeover switch, and the other end is grounded. In the case of dual use as a coater and a decoder, all of these switches S2O9S229S249S269SWO may be provided. According to such a step generator, all the step voltages shown in Table 1 can be generated by operating the switches as shown in Table 2 below.

That is, in the case of a μ-law coater, when switch S22 is closed, resistors 12 and 14 are placed in parallel, resulting in a combined resistance R/2, which becomes the additional resistance on the ground side of the 15 series-connected resistor group RG. When opened, the resistor 10 with resistance value R becomes an additional resistor on the power supply side of the resistor group RG, and the voltage taken out by the switches SWl, SW2, SW3, etc. is, and these are the step voltages of the μ-law coater in Table 1. None other than that.

In the case of an A-law coater, since the switch is opened, the resistor 12 is disconnected, and the additional resistor on the ground side of the resistor group RG becomes the resistor 14 with a resistance value R. Also, the switch S2O is turned on, and the resistor 10 is short-circuited, so the resistor 12 is disconnected. The additional resistance on the power supply side of group RG is zero. In this case, switches SWl, SW2, SW3・
The voltages taken out in ... are the step voltages of the A-law coater in Table 1.

Although the explanation is omitted, the same applies to the decoder. The switches SWO, SWl, SW2, . and coater,
Turns on/off with decoder specified signal. The switch S26 is switched between the positive power source +Vref and the negative power source -Vref depending on whether the step voltage to be generated by the step generator is positive or negative.

This switching is performed by a polarity designation bit added to the digital signal DS2. As explained in detail above, according to the present invention, a step generator consisting of a group of resistors and a group of switches is mass-produced as a general-purpose LS, and the switches are activated by external signals specifying the coater, decoder, A law, and μ law. Since a step generator corresponding to each can be turned on and off, it is possible to mass produce and reduce costs, and the number of resistors used is as small as possible (the number of steps plus four additional resistors), making it more compact. , it is extremely advantageous in terms of high precision, etc.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the configuration of the PCM companding decoder, Fig. 2 is a circuit diagram showing an overview of its hardware, Fig. 3 is a graph for explaining the companding state, etc., and Fig. 4 is the configuration of the PCM companding coater. 5 is a graph for explaining the operation of the coater, FIG. 6 a to d is an explanatory diagram of segments and steps, FIG. 7 is a circuit diagram showing an embodiment of the present invention, and FIG. 8 is a graph for explaining the operation of the coater. This is a circuit diagram showing the wiring as a decoder. In the drawing, SGG is a segment generator, STG is a step generator, DEC is a decoder, COD is a coater, RG is a series resistor group, 10, 16, 12, 14 are additional resistors, S? f:
), S22, S24 are mode changeover switches, SWO, S
Wl... is an output switch.

Claims (1)

[Claims] 1. In the step generator of a companding coder consisting of a segment generator that generates the end point potential of a segment and a step generator that generates a divided potential between both end points of the segment, the same A series resistance group (R_1 to R_n) formed by connecting an additional resistor 10 on the power supply side with a resistance value in series, and an additional resistor 14 on the earth side with the same resistance value as the additional resistor on the power supply side. A first mode selector switch S_2_0 is connected in parallel to the power supply side additional resistor, and another earth side additional resistor 12 having the same resistance value as the earth side additional resistor is connected to the ground side additional resistor. (n+1) output switch groups SW_1 to 2 connected in parallel via the mode changeover switch S_2_2 of No. 2 and turned on and off by a digital signal between each series connection point of the series resistor group and the common output terminal; SW_
1_6, the first mode changeover switch is turned off and the second mode changeover switch is turned on by the μ law designation signal, and the first mode changeover switch is turned on by the A law designation signal, and the second mode changeover switch is turned on by the A law designation signal. A step generator characterized by turning off a mode changeover switch.