JPS58148517A - Encoder - Google Patents

Abstract

PURPOSE:To attain ease of circuit integration with one reference power supply, by determining the state of lower electrodes of main and sub-ladders through switching and sampling input signals again. CONSTITUTION:The main C ladders 1CA-128CA, sub-C ladders 1CB-16CB, main ladder switches SA1-SA8, and sub-ladder switches SB1-SB5 connecting one end in common respectively are provided for an encoder, and a sampling switch 103 is provided between a common connecting point of the ladders 1CA-128CA and inputs. Reset switches 201, 202 are provided between the common connecting point of the ladders 1CA-128CA and 1CB-16CB and ground, and the SA1-SA8 and SB1-SB5 are controlled with a code convesion circuit 105 with SAR. A changeover switch 200 is provided between two potential points a, b of the circuit 105, ground and a reference power supply +Vref. After the state of the lower electrodes is determined, the input signal is sampled again, allowing to simplify the constitution of the encoder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an encoder using a capacitor ladder.

FIG. 1 shows a partial configuration diagram of a companding encoder using a conventional capacitor ladder (hereinafter abbreviated as C ladder). 1st
The figure shows the parts of a currently commonly used μ-1aw 15-line approximation successive approximation feedback encoder, excluding the control system.

101.102 is a ladder reset switch, 103 is a sampling switch, 104 is a converter/4' regulator, 10
5 is a code conversion circuit with SAR, and 106 is a reference power source changeover switch. Main C ladder ICA with binary load, 2c
A, . . . , 128cA have one end connected in common, and are connected to the input via the positive input terminal of the comparator 104 and the sampling switch 1θ3. Further, the other ends of the main C ladders are connected to one ends of the corresponding main ladder switches SAt, . . . t SA8, respectively.

The main ladder switch SA~A8 has three contacts that can be switched.The corresponding contacts are commonly connected, and one is the reference power selector switch 1.
Reference power supply (+vref *-vref) through 06
The other one is grounded, and the remaining one is connected to the negative input terminal of the controller 107. Similarly, binary load sub-C ladders ICB, 2CB...
..., 16CB is also connected at one end in common/? It is grounded via the positive input terminal of the Zuffer amplifier 107 and the ladder reset switch 102. In addition, the basic capacitor cell C is connected between the common connection terminal of the sashi C ladder and the ground.
A capacitor 2CB having a capacitance twice that of B is connected.

The other end of the sub-C ladder is connected to the corresponding sub-ladder switch SB1. . . . is connected to one end of S, 5.

The sub-ladder switches SB1 to SB5 are capable of switching two contacts, and each corresponding contact is commonly connected, and one is the reference power selector switch 1.
06 to the reference power supply, the other one is grounded.

Ladder reset switches 101 and 102 used for discharging the charge of each C ladder are connected between the common electrode of the main C ladder and the sub C ladder and the ground.

The negative input terminal of the buffer amplifier 107 is connected to the output terminal so that it becomes a voltage follower. The output signal of the comparator 104 drives the sign conversion circuit 105 with SAR, and this output drives the main ladder switches SA1 to SA8. Subladder switch SB
1 to SB5 and the reference power source changeover switch 106 are controlled.

Next, the circuit operation will be explained. First of all, capacitor lC
The reset switch 101' of the main C ladder made up of A to 128CA and the reset switch 102 of the sub C ladder made up of 2CB and ICB to 16CB are grounded. At this time, the main ladder switches SA1 to SA8 and the sub ladder switches SB1 to SB5 are connected to the ground side. In this state, the charges in the capacitors of each ladder are discharged and become 'O'.Next, the reset switches 101 and 1
02 is opened and the sampling switch 103 is closed to sample the input signal, and the main C ladder ICA~128
Stores charge in CA according to the input signal. Next, the sampling switch F103 is opened, the polarity of the input signal is determined by the controller 104, and the result is input to the sign conversion circuit with SAR 105, which controls the output SP multiplied signal and the reference power switch 106. do. If the input signal is (→, the changeover switch 106 is connected to the -vref side, and if the input signal is (→, the changeover switch 106 is connected to the +Vref side.'After determining the polarity of vref, the changeover switch 106 is connected to the -vref side. Sequential encoding is performed by the operations of ladder switches SA, -SA8 and sub-ladder switches SB1 -S, 5.

The encoded PCM signal output and the switch status of each ladder have the relationship shown in Table 1. In Table 1, SA, ~SA89SB1 to SB5 in the code conversion output column represent the states of switches with the same symbols in Figure 1, where 0 is ground and 1
indicates that it is connected to Vref, and S indicates that it is connected to the sub-ladder output (v8B).

(b) PCM outputs are Bl, B2. B3. B4. B5. B6. B
7. Consists of 8 bits of B8, B1 is the polarity bit, B8
is the LSB.

Table 1 This type of conventional circuit has the drawback of requiring two types of reference power supplies, positive and negative, in order to encode positive and negative signals as input signals. This is undesirable when converting a conventional encoder into an IC because it leads to an increase in the number of terminals.

The present invention is characterized in that an encoder is configured with one reference power source, and its purpose is to reduce the number of reference power sources and r
This will be explained in detail below by reducing the number of terminals in the C conversion.

FIG. 2 is a partial block diagram of a companding encoder showing a first embodiment of the present invention, and the same components as those shown in FIG. 1 are designated by the same reference numerals. 200 is a changeover switch, 2
01 and 202 are ladder reset switches. For the sake of simplicity, explanations of parts having the same connection relationship as in FIG. 1 will be omitted.

The changeover switch 200 is composed of two circuits and two contacts, and one circuit connects one common contact (indicated by a in the figure) of the main C ladder and sub C ladder to the reference power supply (+vref).
) and ground, and the other circuit switches the other common contacts of the main C ladder and sub C ladder (already shown in the figure) between ground and the reference power source.

The ladder reset switch 201 is inserted between the common electrode of the main C ladder and the ground.
2 is inserted between the common electrode of the sub C ladder and one common contact point (point b in the figure) of the main C ladder and the sub C ladder.

Next, the operation of this circuit will be explained. As an initial state, the second
A changeover switch 200 that determines the state of points a and b in the figure.
Assume that point a is connected to +vrof and point b is connected to ground, as shown by the solid line in the figure.

First of all, as explained in the conventional circuit, the core f sensor I
A reset switch 201 of the main C ladder consisting of CA to 128CA and a reset switch 202 of the sub C ladder consisting of 2cB and 1cB to 16cB are connected to ground. At this time, the main ladder switches S□-SA8 and the sub-ladder switches SB1-SB5 are connected to the ground side (points shown in Figure 2). In this state, the charge in each capacitor is discharged and becomes '-0'.Next, open the ladder reset switch 201 and open the sampling switch 1.
03 is closed, the input signal is sampled, and charges corresponding to the input signal are stored in the main C ladder ICA to 128 CA. Next, open the sampling switch 103, determine the polarity of the input signal with the converter lθ4, and send the result to SA.
input to the sign conversion circuit 105 with R, and its output sp
A changeover switch 200 that determines the states of the double signal, point a, and point b is controlled. If the input signal is negative, the state of the changeover switch 200 remains unchanged from the initial state, and if the input signal is positive, the connection is made so that point a is grounded and point b is connected to +vref.

After determining the state of the changeover switch 200, the sampling switch 103 is closed again to sample the input signal, and then the sampling switch 103 is opened and the ladder reset switch 202 is opened to start the encoding operation.

The relationship between the PCM output, which is the output of the comparator Iθ4, and the states of the main ladder switch S-8 and the sub-ladder switches sB, SIs5 at this time is shown in Table 1 described above.

Sub-ladder buffer amplifier fr when the polarity of the input signal is negative
The output voltage vsB of ov is expressed as follows.

Here, SBi takes a value of 1 or 0 according to Table 1 (b).

Also main C ladder IC ~ 128c con 7 palm A
The voltage Vx at the A-ta 104 human power point is -V
If i, then SAk takes a value of '1' or 0 according to Table 1(a). However, S takes a value of '0'.

According to Table 1(a), SAk' takes a value of 1'' only for S and a value of 0'' for all others.

Next, when the polarity of the input signal is positive, as explained earlier, in FIG. to sample.

At this time, switch SA of main C ladder 1cA to 128cA and Sazo C ladder ICB to 16C6, ~SA8 #S
Since B and ~SB5 remain connected to point b, the electrodes of the main and sub-ladder capacitors on the side connected to the switch (hereinafter referred to as the lower electrode) are at +Vr.
It is connected to 6f. At this time, since the ladder reset switch 202 is connected to point b, the output voltage of the ladder buffer amplifier 107 vs! l is +vrofK
It has become. Next, the ladder reset switch 202 is opened to enter the encoding operation, and the PCM output code and the switch status of each ladder are determined according to Table 1. As mentioned earlier, if the input signal is positive, the Point a is grounded, point b is -
Since it is connected to l-Vr, (, 1 and 0.S in Table 1 means that it is connected to ground and +Vref # v8B, respectively. When the input signal is positive, the sub-C ladder output voltage vlIB' is It is expressed as follows.

Here, Si+i takes a value of 1 or 0 according to Table 1(b).

Also, the voltage Vx' at the input point of the main C U/-ICA to 128CA connector 7 1θ4 is the input voltage y, /
Then... (4) Here, SAk takes a value of 1'' or 0'' according to Table 1(a). However, S takes a value of "0".

According to Table 1 (a), SA has a value of "l" only at S, and all others have a value of 0.

When formula (3) is inserted into the second item in parentheses of formula (4), it can be seen that formula (2) and formula (4) are simply changed in sign.

As explained above, in the first embodiment, a switch is provided to change the state of the lower electrode of the main and sub C ladders, and the input signal is sampled and the switch is switched depending on the polarity of the input signal. By adopting a method in which the input signal is sampled again and encoded after determining the state of the lower electrode, the encoder can be configured with a single reference power source, and there is little need to change the control system for this purpose. There is an advantage that there is no Additionally, there is an advantage that the number of terminals can be reduced compared to the conventional configuration. Furthermore, conventionally, switching between positive and negative power supplies required a bipolar switch, which was difficult to implement, especially when integrated into an IC.However, according to this embodiment, the changeover switch Since unipolarity is sufficient, I
Another advantage is that it is easy to implement when converting to C.

The first embodiment describes the case where a C ladder is used as the sub-ladder circuit, but even when a resistance ladder (hereinafter referred to as R ladder) is used as the sub-ladder circuit, as shown in FIG. Switching the state according to the polarity of the input signal has the effect of making the reference power source of the two encoders single. In FIG. 3, sub-ladder switches SB, ~5B16 are opened and closed according to Table 2. In Table 2, '1' means the switch is closed and '-0' is open.

Further, in the configuration shown in FIG. 4, the same effect can be obtained by switching the switch SP' to the a' side when the input signal is negative and to the b' side when the input signal is positive, depending on the polarity of the input signal.

In this embodiment, the case where the reference power source is +Vref has been described, but it goes without saying that the present invention can be realized using the same concept even when the reference power source is -vref.

Further, the present invention is not limited to companding type encoders, but can be similarly applied to, for example, linear type encoders.

According to the present invention, there is an excellent effect that an encoder that conventionally required two reference power supplies can be realized with one reference power supply.

[Brief explanation of drawings]

FIG. 1 is a partial configuration diagram of a conventional C ladder companding encoder.
FIG. 2, FIG. 3, and FIG. 4 each show a partial configuration diagram of an encoder according to an embodiment of the present invention. 103...Sampling switch, 104...Conn i<
'rater, 105... sign conversion circuit with SAR, 200
...Selector switch, +vr'e f...Reference power supply, ICA~128C...Main C ladder, lCB~
16CB...SU^ C ladder, SA1-SA8...Me, in-ladder switch, SR1-SB5...Sub-rudder switch.

Claims (1)

[Claims] A plurality of capacitors having one end connected in common, a sampling switch that samples and applies an input analog signal to the common connection point, and the other ends of the plurality of capacitors connected to a first connection line and a second connection line. It has a plurality of capacitor changeover switches that are switched and connected, and a control circuit that controls the operation of the capacitor changeover switches, and each of the capacitor changeover switches is switched in response to a control signal '' from the control circuit. In an encoder that changes the potential of the common connection point, and extracts the potential while comparing the change in potential with a ground potential via a comparator to obtain a digital signal from the input analog signal,
A reference power supply changeover switch is provided for switching the potentials of the first and second connection lines to a reference potential and a ground potential, respectively; 1;
An encoder characterized in that an analog-to-digital conversion operation is performed after the reference power supply selector switch is switched according to the polarity of the input signal via the control circuit.