JPS60216630A - Step generator - Google Patents

Abstract

PURPOSE:To constitute a step generator with less number of resistors by controlling on/off of the 1st mode changeover switch and the 2nd mode changeover switch based on the mu rule designation signal or the A rule designation signal. CONSTITUTION:A mode changeover switch S22 is turned on normally, turned off at bit steal, a mode changeover switch S24 is turned off normally and turned on at bit steal based on the mu rule designation signal. The mode changeover switch S22 is turned on and the mode changeover switch S24 is turned on by the A rule designation signal. Switches SW0-SW16 are turned on/off by a low-order bit of a digital signal.

Description

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

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

The decoder used for this is shown in Figure 1 of Tsutomi.
It consists of a segment generator SGG and a step generator STG, and the former has a segment Si (+=1.2
．． . . . 8) generates an analog voltage A indicating the starting point P1 of the sect, and the latter indicates the starting point P1, the ending point P1 . A voltage B is generated by dividing the voltage between P2. In PCM, when encoding, the small amplitude part is enlarged in order 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. 8
When the bit input signal DS is input, the control circuit CNT supplies the upper bits thereof to the segment generator SGC to generate the starting end potential A of the segment Si in the order determined by the bits, and also generates the lower bits in steps. A divided potential B defined by the plurality of bits is generated. These are added and the sum becomes the output analog signal AS2.

Specifically, as shown in Fig. 2, the segment generator SGC
consists of variable capacitors 01 to C3, and step generator STG consists of variable resistors R1 and R2. Each of the capacitors 01 to C3 includes a plurality of capacitors and a switch that is opened and closed by the digital input signal DS to insert and remove the capacitors. When the switch is opened and closed by the digital signal SD2 and the values of the capacitors C1 and C2 change, the divided potential of the reference voltage Vref by these changes, and thus the voltage A
is output. The variable resistors R1 and R2 consist of a large number of series resistors and a switchgear group arranged between their series connection point and the output end and turned on and off by a digital input signal.
The switch is turned on and off by the input signal DS2 to output a divided voltage B' of the reference voltage Vref. This voltage B' is a voltage determined by the lower bit of the signal DS2, which is unrelated to the segment order r (t-t+ 2...8), but is determined by the slope of each segment as shown in FIG. are different, and therefore the required step voltage should vary depending on the segment order. Capacitor C3 performs this correction. The switch group for inserting and removing the capacitor C3 is also turned on and off by the upper bits of the input signal DS2, changing the capacitance of the capacitor and controlling the voltage B' added to the voltage A.
Correct it to

As shown in FIG. 4, the COG used for PCM transmission consists of a comparator COMP, a successive approximation register SCR, and a local decoder DEC. This local decoder DEC has the same structure as the decoder described above. When an input signal As+' having a value as shown in FIG. 5 is input to the comparator COMP, the decoder DEC outputs Ov2 at first, so the comparator outputs an H level, and the register SCR receives this and outputs the full scale F. An 8-bit digital signal DS+ commanding 1/2 voltage is output to the decoder DEC.

Therefore, the decoder DEC outputs a voltage of 0.5F to the comparator COMP, and since 0.5F>AS+, the output of the comparator becomes L level.

In response to this (b), the register SCR outputs a digital signal DS+ commanding a voltage of 1/2 of 0.5 F, and the outputs of the decoders D and E C become 0.25 F. 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/
produces an output commanding a voltage of 2. Similarly, the decoder output approaches the input analog voltage AS+ as much as possible, and the H, L (1,
Since 0) indicates the digital code of the analog signal AS+, this is the coded output of the input signal.

For signal companding, A side (A Law) and μ law (μ La
There is w). These are of course well-known, but to briefly explain, on the A side, the full scale F is set to 1/2.1/4.1/, 8, etc. as shown in Figure 6 fa). Segments Se, St, 36 old...sl. Also, according to the μ law, the segment S2 is twice the minimum segment s1,
Segment s3 is twice that, and segment SB is created in the same manner, and S + +S 2+ . . . +Se becomes full scale F. The method of dividing one segment is also different between the A side and the μ law. In other words, on the A side, the same figure (C)
The whole is divided into 32 parts as shown in the figure, and in the case of Korg it is 2/3.
2. /4/32. In the case of a decoder, the point 6/32... is 1/32.3/32.5/'32...
. . . is defined as each step. In the case of μ law, the same figure (d
One segment is divided into 33 as shown in l, and in the case of Korg, the point is l/33.3/33, old..., and in the case of decoder, it is 0/33.2/33°4/33... Let the point . . . be each step. The step generator STG described above outputs each of these step voltages. The above is summarized in Table 1 as follows.

Table 1 Korg decoder By the way, Korg decoder step generator ST
Conventionally, G was created exclusively for the A-law and the μ-law, and was never shared. However, the step generator is also currently L
Although integrated circuits are integrated, they can be mass-produced to reduce costs, so they should be commonly manufactured as general-purpose products as much as possible.
It is preferable to increase the scale of production.

A 1111, the μ-law dual-use step generator uses 33 resistors because the number of divisions of one segment is 33 at maximum as is clear from the table above, and if they are connected in series and a reference voltage is applied, each series connection point If one resistor is removed to make 32 resistors, each step voltage of A-law can be obtained from each series connection point. However, this only uses 33 resistors to obtain a step voltage of 16111i1, and since there are many resistors, a large area is required, and there is variation, making it 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 16 taps.The present invention is characterized by generating the end point potential of the segment. In the step generator of the companding decoder, 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. n
A series resistance group formed by connecting resistors in series (n is a natural number) and a ground side additional resistor having the same resistance value as the power source side additional resistor are connected in series, and the power source side additional resistor is connected to the power source side additional resistor. Connect another power supply side additional resistor with the same resistance value as the ground side resistor in parallel via the first mode selector switch, and connect the ground side A1 resistor to the ground side (; Another ground side of the resistance value (=J) is connected in parallel via a second mode selector switch, and a digital signal is connected between each series connection point of the series resistance group and between the ground and the common output terminal. A group of (n + 2) output switches that are turned on and off is provided, and according to the μ-law designation signal, the first mode changeover switch is turned on when the lightning is turned on, turned off during pit steal, and the second mode changeover switch is turned on. The energization is turned off and turned on during pit steal, and the first mode changeover switch is turned on and the second mode changeover switch is turned on by the A-law designation signal. This will be explained in detail with reference to an example.

FIG. 7 shows the connections for the cog of an A/μ compatible step generator, and FIG. 8 shows an embodiment of the invention and shows the connections for the decoder of the same generator.

Both the case for the Korg in FIG. 7 and the case for the decoder in FIG. 8 are the same resistors with a resistance value R (also R or R+).

In this embodiment, 15 resistors (represented by R2...Rn) are connected in series, and in the case of a Korg, resistors 10, 12, and 14, each having a resistance value R, are connected in series at both ends. connects resistors 10 and 16 and 12 and 14 of resistance value R in series. Therefore, if the resistor is to be used as both a coder and a decoder, it is sufficient to use the configuration shown in FIG. 8 as the resistor. Output switches SW1, SW2, . . . , SW, 6 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 S20 that short-circuits the resistor 10 in the case of Korg.
In the case of a decoder, a mode changeover switch 324 which disconnects the resistor 16, a mode changeover switch S22 which disconnects the resistor 12, the switch S22, and a switch S W a which grounds the output terminal 20 are provided. In both the coder and the decoder, one end of the additional resistor is connected to the positive and negative reference voltage sources ±V ref via the changeover switch S26, and the other end is grounded. Coorg.

For dual-use decoder switches, these switches S20.322.324.326, SW.

All you have to do is set them up.

According to such a step generator, the switch can be set as shown in Table 2 below.
All the step voltages shown in Table 1 are generated by operating as shown in Table 2. Korg μ law S22 ON S20 OFF A law S22 OFF 320 ON Deterder μ law S22 OFF 324 ON μ law 322
ON 324 OFF (bit 5teal) A-law S22 ON 324-ON In other words, in the case of μ-law coder, when switch 322 is closed, resistors 12 and 14 become parallel, so their combined resistance is R/2
This becomes the additional resistance on the ground side of the 15 series-connected resistor group RG, and when the switch 520 is opened, the resistor 10 with the resistance value R becomes the additional resistance on the power supply side of the resistor group RG, and the switches SW1. The voltage taken out by SW2゜SW3... is Vref・/ (+16R) =Vrei
-2233 Vrei (-+R) / (+16R) = νref
・-2233 Vref・(+2R) / (+16R) -Vref
-2233, and these are nothing but the step voltages of the μ-law coder in Table 1. In the case of the A-law coder, the switch S22 is opened, so the resistor 12 is disconnected, and the additional resistor on the ground side of the resistor group RG becomes the resistor 14 with the resistance value R. Also, the switch S20 is turned on, and the resistor 10 is short-circuited. On the power supply side of resistor group RG (additional resistance is zero. In this case, switch SWI,
The voltages taken out by SW2, SW3, . . . are as follows, and these are nothing but the step voltages of the A-law coder in Table 1. Although the explanation is omitted, the same applies to the decoder.

Switch SWo, SW+.

SW2...5w16 is the digital signal DS mentioned above.
Switch S20 is turned on and off by the lower bit of 2.

S22. S24 is turned on and off by A, μ law, Korg, and decoder designation signals. The switch 326 selects a positive voltage fB depending on whether the step voltage to be generated by the step generator is positive or negative.
+Vref, through current, switched to source -Vref. 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 LSI, and the switches are turned on and off by external signals specifying the Cog, decoder, A-law, and μ-law. Since step generators corresponding to each type can be made, mass production is possible, and therefore costs can be reduced.Also, the number of resistors used is as small as possible (the number of steps plus four additional resistors), so miniaturization is possible.
This is extremely advantageous in terms of high precision, etc.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the configuration of the PCM companding decoder, Figure 2 is a circuit diagram showing an overview of its hardware, Figure 3 is a graph for explaining the companding state, etc., and Figure 4 is an overview of the pcM companding decoder configuration. 5 is a graph for explaining the operation of Korg, FIG. 6 +a) to (dl is an explanatory diagram of segments and steps, FIG. 7 is a circuit diagram showing connections for Korg,
FIG. 8 is a circuit diagram showing an embodiment of the present invention. In the drawing, SGG is a segment generator, STG is a step generator, DEC is a decoder, COD is a Korg, RG is a series resistor group, 10, 16, 12.14 are additional resistors, and S20
, S22, , S24 are mode changeover switches, SW
n, SW+... are output switches. Applicant Fujitsu Ltd. Representative Patent Attorney Minoru Aoyagi Figure 2 Figure 3 SGG STC, "" Input

Claims (1)

[Claims] In the step generator of the companding decoder, which is composed of a segment generator that generates an end point potential of a segment and a step generator that generates a divided potential between both end points of the segment, the same voltage is connected between the power terminal and the ground terminal. A series resistance group (R+ to Rn) formed by connecting an additional resistance on the power supply side (10) in series with n resistors (n is a natural number), and an additional resistance on the earth side with the same resistance value as the additional resistance on the power supply side. A resistor (14) is connected in series, and another power supply side additional resistor (16) having the same resistance value as the power supply side additional resistor is connected in parallel with the power supply side additional resistor via a first mode changeover switch (S24). , and connect another ground side resistor (12) having the same resistance value as the ground side additional resistor to the ground side additional resistor (12) in parallel via the second mode changeover switch (S22). A signal (n+2
) output switch groups (SWo"SW 16 ) are provided, and according to the μ-law designation signal, the first mode selector switch is normally on, off during pit steal, and the second mode selector switch is normally off. , the step generator is turned on during a pit steal, and the first mode changeover switch is turned on and the second mode changeover switch is turned on in response to an A-law designation signal.