JPH03759Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is based on a digital-to-analog system in which, for example, a plurality of constant current sources are provided, and an analog conversion signal is obtained by selectively outputting and adding the constant current sources according to an input digital signal. It relates to current switching devices used in converters and the like.

In the conventional _current switching device of this kind, as shown in _{FIG .} The drain of Q ₂ is output terminal 1
3.14. This differential FET switch 1
A differential switch drive circuit 16 is provided to drive the switch 5. In the differential switch drive circuit 16, the emitters of NPN transistors Q ₃ and Q ₄ are connected together and connected to the power supply terminal 12 through a constant current source 17, and the collectors of each are connected to resistors 18 and 1, respectively.
It is connected to the power supply terminal 21 through 9. The bases of the transistors Q ₃ and Q ₄ serve as input terminals 22 and 23, and a switching signal is applied between these input terminals 22 and 23. The output terminal of the switch drive circuit 16 is the collector of the transistor _Q3 , which is a differential type
One input terminal 25 of the FET switch 15, i.e.
Connected to the gate of FETQ ₂ . The other input terminal 24 of the differential FET switch 15 is connected to a variable power supply 26.

When a switch control signal is applied so that input terminal 22 is on the negative side and terminal 23 is on the positive side, transistor Q ₃ is turned off, transistor Q ₄ is turned on, and input terminal 25 becomes at a higher level than input terminal 24. FETQ ₂ becomes conductive and FETQ ₁ turns off.
Conversely, when a control signal is applied that sets input terminal 22 on the positive side and input terminal 23 on the negative side, transistor Q ₃
is turned on and the gate of FETQ ₂ is connected to input terminal 24.
FETQ ₂ turns off as the level becomes lower than
FETQ ₁ turns on. In this way, the constant current of the constant current source 11 can be switched and supplied to the output terminal 13.

In order to perform this operation correctly, the following adjustments are made. First, turn off transistor _Q3 and apply the power supply voltage of terminal 21 to terminal 25.
Turn on FETQ ₂ , adjust the voltage of power supply 26 in that state, gradually lower the potential applied to terminal 24,
Do this until FETQ ₁ turns off. Thereafter, transistor Q ₃ is turned on, and the current of constant current source 17 is gradually increased until FET Q ₂ is turned off. In this way, the voltage applied to the input terminal 24 is
FETQ ₂ is turned on when the voltage of ΔV is high, and when input terminal 25 is lower than input terminal 24 by ΔV, FETQ ₁ is turned on.

In this way, the current switch shown in FIG. 1 requires adjustment at least twice, but in reality, even when setting the voltage of the power supply 26 for the first time, it is not always possible to obtain a good value with just one adjustment. It is necessary to make repeated adjustments, so in order to use a current switch to turn on and off the output of multiple current sources like the DA converter mentioned above, all of the current switches must be used. The disadvantage is that it requires a lot of effort to adjust.

On the other hand _, in the prior art, as shown in FIG. 2 _with the same reference numerals assigned to parts corresponding to those in FIG. 24
Some are connected to each other. In this case, when one collector of transistors Q ₃ and Q ₄ in the switch drive circuit is at a high level, the other collector is at a low level, so the on/off state of transistors Q ₃ and Q ₄ in the switch drive circuit is By switching, the on/off states of FETQ ₁ and Q ₂ can be switched.

Adjustment of the switch operation in this case involves, for example, turning on the transistor Q ₃ and turning off the transistor Q ₄ to set the current of the current source 17 to zero.
FETQ ₁ and Q ₂ are both in the on state, and from this state the current of the current source 17 is increased, and along with this,
Increase the current until the potential of FETQ ₂ drops and FETQ ₂ turns off. This circuit has the characteristic that only one adjustment is required. However, the gate of FETQ ₁ connected to the output terminal 13 side, that is, the input terminal 24
The gate potential changes every time the FET switch 15 switches, and this appears as spike-like noise at the output terminal 13, which has the disadvantage of deteriorating the quality of the output waveform.

This idea is easier to adjust than above, and a constant voltage is applied to the gate of the FET on the output side.
The present invention provides a current switch that does not cause spike noise to be mixed into the output.

Next, a third example of the current switching device according to this invention will be described.
This will be explained with reference to the figures. In FIG. 3, parts corresponding to those in FIGS. 1 and 2 are given the same reference numerals. In this embodiment, the input terminals 24 and 25 of the differential FET switch 15 are connected to the resistor elements 2 and 25, respectively.
It is connected to the power supply terminal 21 through 8 and 29. A variable current distribution circuit 31 is also provided. That is, the variable current distribution circuit 31 is composed of NPN transistors Q ₅ and Q ₆
The emitters of these transistors Q ₅ and Q ₆ are connected to the power supply terminal 12 through a variable current source 17, and in this example, their bases are connected to each other and connected to the power supply terminal 32. transistor
A current that is 1/2 of the current of the current source 17 is output to Q ₅ and Q ₆ , respectively. The output current can be increased or decreased while maintaining this distribution ratio.
One of the distributed currents, ie, the collector current of transistor Q ₅ , is supplied to resistive element 28 . Therefore, the collector of this transistor _Q5 is FET switch 1
It is connected to the input terminal 24 of No. 5. The other of the distributed currents, that is, the collector current of transistor _Q6 , is supplied as a switching current to the differential switch drive circuit 16, that is, the collector of transistor _Q6 is connected to the emitters of transistors _Q3 and _Q4 . The resistance value of the resistance element 28 is R ₁ , and the resistance value of the resistance element 29 is R ₂
and R ₁ = 1/2R ₂ .

In this configuration, to adjust this current switch, turn off FET Q ₂ and turn on FET Q ₁ , that is, turn on transistor Q ₃ , and in this state, current source 17
Increase the current I from zero. That is, initially, the input terminals 24 and 25 of FETQ ₁ and Q ₂ are supplied with the voltage of the power supply terminal 21, and are both in the on state.
As the current I is increased, the voltage drop across the resistive element 29 is twice as high as the voltage drop across the resistive element 28 due to the previously mentioned resistance value;
Initially, the voltage at terminal 24 and the voltage at terminal 25 are equal, but as the current I increases, the voltage at terminal 25 drops below the voltage at terminal 24, and as the difference becomes larger, FETQ ₂ is turned off and FETQ ₁ is turned off. turns on.
The adjustment is completed in this state, but at this time, the terminal 24 is higher than the terminal 25 by ΔV.

At this time, the voltage at terminal 24 is I/2R, and the voltage at terminal ₂₅ is 1/2IR ₂ = I/2×2R ₁ , and the voltage ratio of these terminals 24 and 25 is V _g1 /V _g2 = 1/2. At this time, When the switch drive circuit 16 is reversed and transistor Q ₃ is turned off and transistor Q ₄ is turned on, the terminal 25 side becomes the first ΔV with respect to the terminal 24.
becomes large, FETQ ₂ turns on and FETQ ₁ turns off.

The characteristics required for the current selector switch 15 are as shown in _FIG .
When the current of the current source 11 is small _, the potential difference V _g1 -V _g2 between 4 and 25 is symmetrical to V _g1 as shown in curves 34 and 35, and the current When the current of the source 11 is large, as shown in curves 36 and 37, they are the same and symmetrical, and their rise and output current I ₀
The required input until each reaches a constant current I _s ,
In other words, the minimum value of the voltage change at the terminal 25 with respect to the terminal 24 increases as the current I _s increases.

As described above, such a relationship can be obtained by one adjustment by increasing the current I of the current source 17 from 0 with FETQ ₂ turned off. Furthermore, during the current switching operation, the voltage V _g1 at the terminal 24 is given a constant value, so that no spike noise occurs at the output terminal 13 due to the current switching operation.

The variable current source 17 may be omitted from the variable current distribution circuit 31, and instead, as shown in FIG. 5, a variable resistor 38 may be connected to change its resistance value. In addition, in the configurations of FIGS. 3 and 5, for example, as shown in FIG. 6, a variable resistor 39 is connected between the emitters of transistors Q ₅ and Q ₆ in the current distribution circuit 31.
It is also possible to connect both ends of the variable resistor 39 and connect the mover of the variable resistor 39 to the variable current source 17 to adjust the variable resistor 39 to equally control the currents flowing through the transistors Q ₅ and Q ₆ . Furthermore, in the above description, the resistance value of the resistance element 29 is twice that of the resistance element 28, but the resistance values of the resistance elements 28 and 29 are assumed to be the same value,
The current distribution circuit 31 may be configured so that the current flowing through the resistive element 29 is twice the current flowing through the resistive element 28. In short, it is only necessary to make the voltage drop occurring in the resistance element 29 larger than the change in the voltage drop occurring in the resistance element 28. differential type
A differential transistor switch may be used instead of the FET switch 15. In other words, bipolar transistors may be used instead of FETQ ₁ and Q ₂ .

[Brief explanation of the drawing]

Figures 1 and 2 are connection diagrams showing a conventional current switch, Figure 3 is a connection diagram showing an example of the current switch according to this invention, and Figure 4 is the output for the input of the current switch in Figure 3. A current characteristic diagram, FIG. 5 is a connection diagram showing another example of the variable current distribution circuit, and FIG. 6 is a connection diagram showing another example of the current switching device according to this invention. 11: constant current source, 12: power supply terminal, 13: output terminal, 15: differential FET switch, 16: switch drive circuit, 17: variable current source, 31: variable current distribution circuit.

Claims (1)

[Scope of utility model registration request] Switching is controlled by a differential semiconductor switch, a constant current source connected to a common connection terminal of the differential semiconductor switch, and a switch control signal, and one output terminal is connected to the first input terminal of the differential semiconductor switch. In the current switching device, the current switching device includes a differential type switch drive circuit connected to the differential type semiconductor switch, and first and second resistors respectively connected between the first and second input terminals of the differential type semiconductor switch and the power supply terminal. and a current distribution circuit that can change the output current while maintaining the distribution ratio, one distribution current of the current distribution circuit is supplied to the switch drive circuit as a switching current, and the current distribution circuit of the current distribution circuit is supplied as a switching current to the switch drive circuit. The other distributed current is supplied to the second resistance element, and due to a change in the current in the current distribution circuit, the change in voltage drop across the first resistance element and the second resistance element is greater in the first resistance element. The current switching device is selected as follows.