JPS6217416B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DA converter that converts a digital value into an analog value using a resistance ladder network, and is particularly intended to reduce the influence of variations in its constituent resistance elements.

[Prior art]

Figure 1 shows a current mode DA converter using a conventional RADAR network. Section L ₁ L ₂ consisting of series resistor 11 and giant resistor 12...
...Rada network 13 with Ln connected in series
One end of the ladder network 13 is connected to a constant current source 14, and the other end is connected to the other end of the constant current source 14, a common potential point, through a resistor 15. Each section of Radha Network 13 L ₁ ~
The other ends of the shunt resistors 12 Ln are connected to the movable contacts of the changeover switches S ₁ to Sn, respectively. One fixed contact of each of the changeover switches S ₁ to Sn is connected to a common potential point, and the other fixed contact of each switch is connected to the operational amplifier 1.
Connected to the inverting input side of 6. A feedback resistor 17 is connected between the output side of the operational amplifier 16 and its inverting input side, and the non-inverting input side of the operational amplifier 16 is connected to a common potential point.

The resistance value of each series resistor 11, resistor 15, 17 in the RADAN network 13 is set to R, and the resistance value of each shunt resistor 12 in the RADAN network 13 is set to 2R. The changeover switches _S1 to Sn are controlled by each corresponding bit of the binary input digital value, and when the bit is "0", they are connected to the common potential point, and when the bit is "1", they are connected to the inverting input side of the operational amplifier 16. . The most significant bit MSB of the n-bit input digital value controls the changeover switch _S1 , and the least significant bit LSB controls the changeover switch Sn. The currents i ₁ -in flowing through each shunt resistor 12 of sections L ₁ -Ln are binary weighted. In this case, in order to obtain high conversion accuracy, it is necessary to make each resistance value of the resistors 11 and 12 highly accurate.

[Summary of the invention]

The purpose of this invention is to provide a DA converter that can average out variations in resistance values and obtain highly accurate conversion outputs by replacing sections of a RADAR network at a sufficiently high speed compared to changes in input digital values. There is a particular thing.

According to an example of the present invention, N sections consisting of series resistors and shunt resistors are sequentially connected in a ring shape through disconnection switches, and a shorting switch is connected in parallel with the series resistor of each section, A movable contact of a changeover switch is connected to the other end of each shunt resistor, and one fixed contact of these movable contacts is connected to a common potential point, and the other fixed contact is connected to a common output terminal in the case of a current mode type. In the case of voltage mode type, it is connected to a common power supply. Further, the connection point of each section is connected to a constant current source through a power supply switch in the case of a current mode type, and to a common output terminal through an output switch in the case of a voltage mode type.

One of the disconnection switches is turned off, the feed switch (or output switch) connected to one side of the disconnection switch is turned on, and the transfer switch connected to the other side is connected to a common potential point and its The shorting switches of the adjacent sections on the side whose changeover switches are connected to the common potential point are turned on. Furthermore, corresponding to each bit of the input digital value, each changeover switch is selectively connected. The setting state of each switch is maintained by maintaining the relative position of the section on the ring, turning off the disconnection switch one after another at a constant cycle, and controlling the other switches by a switch control section. By this switch control, the positions of the sections are sequentially changed, and the variations between the sections are averaged out.

[First Embodiment] FIG. 2 shows an example in which the present invention is applied to a current mode type, in which eight resistors 11 having a resistance value R are sequentially connected to one each of disconnection switches _S9 to _S16 . They are connected in a ring shape, and one end of a resistor 12 with a resistance value of 2R is connected to one connection point between each disconnection switch and the resistor ₁₁ . A Rada network is constructed in which ₈ are connected in a ring shape. Each resistor 11 is connected in parallel with one shorting switch S ₁₇ to _{S 24} . The connection points of the resistor 11 and the disconnection switch at the connection points of each section are connected to a constant current source 14 through power supply switches _S1 to _S8 , respectively. The other end of each resistor 12 is a changeover switch S ₂₅ to _{S 32}
One fixed contact of each of the changeover switches S ₂₅ to _{S 32} is connected to a common potential point, and the other fixed contact of each switch S 25 to S 32 is connected to the output terminal 18 .

One disconnection switch _S16 is turned off, the power supply switch _S1 at one end of the disconnection switch _S16 that has been turned off is turned on, and the changeover switch _S32 at the other end is connected to a common potential point. The short-circuit switch S ₂₃ of the adjacent section on the side connected to the common potential point is turned on with the changeover switch S ₃₂ of the disconnection switch S ₁₆ which has been turned off. When one disconnection switch S ₁₆ is turned off, a ladder network consisting of the cascade connections of sections L ₁ to L ₇ is formed, of which section L ₁ at one end is connected to the power supply 14 and section at the other end is connected to the power supply 14.
In L ₇ the resistor 11 is shorted by the shorting switch S ₂₃ and the resistance R in the resistor 12 of section L ₈
and the resistor 12 of section _L7 constitute one section as a ladder network, and is terminated at the resistance value R in the resistor ₁₂ of section L8.

When one disconnection switch _S16 is off, the changeover switch _S25 on the power supply 14 side of the Rada network, that is, section _L1 , is controlled by the most significant bit of the input digital value, and is controlled by the least significant bit of the input digital value. The changeover switch _S31 of the final stage section _L7 is controlled. Similarly, the changeover switches _S26 to _S30 of sections _L2 to _L6 are controlled in accordance with each corresponding bit of the input digital value. For example, when the input digital value is 101000, the changeover switches S ₂₅ and S ₂₇ are set to the output terminal 10 side. As the disconnection switches to be turned off are sequentially switched, as the seven sections of the radar network are sequentially circulated, the output terminal side of each changeover switch also changes its position relative to the disconnection switch on the ring. The changeover switch, which is held and switched, and which is placed on the common potential point side of the power supply switch that is similarly turned on, is also switched while maintaining its relative position with respect to the disconnection switch that is turned off. FIG. 3 shows an example of a time chart of the switch control in FIG. 2 when the input digital value is 101,000.

[Switch control section]

An example of a switch control section that controls the switch in this manner is shown in FIG. The control section is switch S ₁ ~ S ₃₂
a constant control section 21 that controls the changeover switch _S25 to
The constant control section ₂₁ includes, for example, a D-type flip-flop FF ₁ to
FF ₈ are connected in cascade, and the Q output of the final stage flip-flop FF ₈ is fed back to the data terminal D of the first stage flip-flop FF ₁ , and a high level "1" is applied to the preset data terminal A of the first stage flip-flop FF ₁ . given other flip-flops FF ₂ ~
A low level "0" is given to the preset data terminals A of FF ₈ , respectively, and flip-flops FF ₁ to
It is a circular shift register that performs a shift operation every time a clock is applied from the terminal 23 to the clock terminal of _FF8 .

As shown in FIG. 3A, when the load terminal 24 _is
When a load command is given to each preset terminal P of flip-flops _FF1 to _FF8 , flip-flop _FF1 is preset to "1" and the others are preset to "0", and this data pattern "100...0" is applied to the third
Shifted every clock at terminal 23 shown in Figure B,
The Q outputs Q ₁ -Q ₈ of flip-flops FF ₁ -FF ₈ change as shown in FIGS. 3C-J, respectively. The period of this clock is T, and the flip-flop
The outputs of each Q output _Q1 to _Q8 of _FF1 to _FF4 are connected to the power supply switches _S1 to _S8 , _S23 , _S24 , S17 to _S17 in FIG.
_{S22 is} controlled, and the _{disconnection switch} in _FIG .
S ₁₆ , S ₉ to S ₁₅ and changeover switches S ₃₂ and S ₂₅ to _{S 31} are controlled, respectively. Control of the changeover switches S ₂₅ to _{S 32} is performed by outputting an AND with the corresponding control signal from the output control section 22, and a high level is set to the output terminal 18 side, and a low level is set to the common potential point side. Ru.

Similarly to the constant control section 21, the output control section 22 also constitutes a circular shift register by cascading D-type flip-flops _FF9 to _FF16 , and a shift operation is performed by the clock at the terminal 23 to synchronize with the constant control section 21. Be taken. The load command from the terminal 24 is also given to the preset terminals P of the flip-flops FF ₉ to FF ₁₆ , and this load command causes each bit data of the input digital value stored in each bit 15 ₁ to 15 ₈ of the register 25 to be read. For example, "10100000" is preset to flip-flops _FF9 to _FF16 . Each Q output of the flip-flops FF ₉ to FF ₁₆ (K to R in FIG. 3) and the output to control the changeover switches S ₂₅ to S ₃₂ from the constant control section 21 are ANDed.
The circuits ₁₁ to ₁₈ perform logical AND operations to control the switches _S25 to _S32 , respectively.

The RADAN network connected in a ring shape as described above is disconnected at one point by a disconnection switch, a current mode RADAN network DA converter is configured, and its analog output is output.
Since the disconnection switches that are turned off are sequentially moved, the ladder network is also sequentially rotated one section at a time. Therefore, the weight currents obtained from each section can also be sequentially switched. By averaging the output of the output terminal 18 by the smoothing circuit 26, variations between the sections are averaged. Each section consists of a series resistor 11 and a shunt resistor 12, and since there are variations between them, one of all the resistors in the ladder network is made variable, and the shunt resistors 11 and 12 are made variable. If the ratio is adjusted during rotation so that the ratio is 1:2, there is no need to adjust the resistance values of many other resistors 11 and 12 with high precision. Even if there is variation in the resistors 11 and 12, it is small to begin with, so
The smoothing circuit 26 may be extremely simple, consisting of one capacitor and one resistor. In this way, the resistors 11 and 12 do not need to be of high precision, so the resistors 11 and 12 are installed in the semiconductor integrated circuit.
can be incorporated, and the DA converter can be configured as a semiconductor integrated circuit. disconnection switch,
As the power supply switch, changeover switch, etc., analog switches made of field effect transistors can be used.

[Second Embodiment] In the example shown in _FIG .
~S ₁₆ Each weight current is affected by the on-resistance of other switches. To eliminate this effect,
Using the prior art method, one of the transistors Tr ₁ to _{Tr 8} is connected to the opposite side of the disconnection switch of each shunt resistor 12, as shown in FIG. The collectors of the transistors are connected to the movable contacts of the changeover switches _S25 to _S32 , respectively. Power supply 2 to each base of transistors Tr ₁ to Tr ₃
A constant voltage is applied from 7. Therefore, a constant current flows through each of the transistors Tr ₁ to _{Tr 2} with a weight depending on the connection state of the resistor connected to the emitter side at that time. For example, in Figure 5, the power supply switch
When S ₁ is on, changeover switch S ₃₂ is connected to the common potential point, and isolation switch S ₁₆ is off, the constant current flowing through transistor Tr ₁ is
A half current flows through Tr ₂ to Tr ₃ in sequence. Also, this figure shows when the input digital value is 0100000, the selector switch _S26 is on the output terminal 18 side, and the selector switch S26 is on the output terminal 18 side.
S ₂₅ , S ₂₇ to _{S 32} are placed on the common potential point side.

[Third Embodiment] Figure 2 shows a current mode ladder network type DA.
Although the present invention is applied to a converter, it can also be applied to a voltage mode ladder network type DA converter. An example of this is shown in FIG. 6, in which parts corresponding to those in FIG. 2 are given the same reference numerals. In this case, each output switch
S ₃₃ to _{S 40} are connected between each connection point of the resistors 11 and 12 and the common output terminal 18, respectively. Further, the end of each shaft resistor 12 opposite to the resistor 11 is connected to a movable contact of a changeover switch _S25 to _S32 , and these changeover switches _S23 to _S32 are connected to a common potential point and a constant voltage source 28, respectively. It is switched and connected to. When one disconnection switch, e.g. S ₉ , is off, the output switch S ₃₃ on one side thereof is on, the changeover switch S ₃₂ on the other side is connected to a common potential point,
Furthermore, the shorting switch _S23 of the first stage _L7 of the Rada network at that time is turned on at the same time, and these disconnection switches _S9 to _S16 , output switches _S33 to _S40 , changeover switches _S25 to _S32 , and shorting switch S ₁₇ to _S24 are controlled by the constant control section 21, and the changeover switches _S25 to _S32 are controlled by the output control section 22 according to the corresponding bit of the input digital value, and when the input bit is "1", the corresponding changeover switch is Connect to the power supply 28 side.
The section connected to output terminal 18 is made to correspond to the most significant bit of the input digital value. In the example shown in Figure 6, "1010000" is input, and when the disconnection switch _S9 is off, the changeover switch is
S ₂₅ and S ₂₇ are connected to power supply 28 .

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional DA converter, Figure 2 is a circuit diagram showing a conventional DA converter.
The figure is a circuit diagram showing an example of applying the present invention to a current mode DA converter, Figure 3 is a time chart showing an example of control signals for each switch in Figure 2, and Figure 4 is an example of a switch control section. 5 is a circuit diagram showing another example of the present invention, and FIG. 6 is a circuit diagram showing an example in which the present invention is applied to a voltage mode type DA converter. 11: Resistor with resistance value R, 12: Resistor with resistance value 2R, 14: Constant current source, 18: Output terminal, 2
1: constant control section, 22: output control section, 26: smoothing circuit.

Claims (1)

[Scope of Claims] 1. A series circuit of a disconnection switch, a first resistance element, and a shorting switch connected in parallel, one end of which is connected to one end of the series circuit, and a resistance value twice that of the first resistance element. N stages (N is an integer of 3 or more) of this section are connected in a ring shape, and the connection point of each section is connected to one end of the power supply through a separate power supply switch. A movable contact of a changeover switch is connected to the other end of each second resistance element of each section, one fixed contact of each of these changeover switches is connected to a common output terminal, and the other fixed contact is connected to a common output terminal. turning off a disconnect switch in one of the sections connected to the other end of the power supply;
The power supply switch connected to one end of the disconnection switch that was turned off is turned on, the changeover switch connected to the other end is connected to the power supply side, and the other end of the disconnection switch that is turned off is turned on. Turn on the short circuit switch of the adjacent section, connect the above changeover switch to the power supply side or the output side according to each corresponding bit of the input digital value, and change the setting state of these switches to the relative position on the above section ring. A DA converter is provided with a switch control section that repeatedly turns off each of the above-mentioned disconnection switches at a constant period so as to maintain the disconnection switch. 2. A series circuit of a disconnection switch, a first resistance element and a shorting switch connected in parallel, and a second resistance element having one end connected to one end of the series circuit and having a resistance value twice that of the resistance element. A section is constructed, and N stages (N is an integer of 3 or more) of this section are connected in a ring shape, and the connection points of each section are connected to a common output terminal through separate output switches, respectively. A movable contact of a changeover switch is connected to the other end of each second resistance element of the section, one fixed contact of each of these changeover switches is connected to one end of a common power supply, and the other fixed contact is connected to the other end of the power supply. Turn off the disconnect switch connected to one of the sections, turn on the output switch connected to one end of the disconnect switch that was turned off, and turn on the output switch connected to the other end of the disconnect switch. Turn on the short-circuit switch of the section adjacent to the one end side of the disconnection switch that was turned off, and switch the changeover switch to one end or the other end of the power supply, depending on each corresponding bit of the input digital value. A switch control section is provided which is connected to the end of the disconnection switch and repeatedly turns off the disconnection switches at regular intervals so as to maintain the relative positions of the switches on the section ring. DA converter.