JPH04183015A - Mosfet resistor circuit - Google Patents

Abstract

PURPOSE:To easily enlarge the range of a variable resistance value by automatically changing the state of connecting plural MOSFET (field effect transistors) corresponding to a realizing resistance value. CONSTITUTION:This circuit is equipped with an input signal terminal 25, an output signal terminal 26, a clock signal input terminal, analog switches 27 and 28, a bias voltage setting circuit 30, a MOSFET switching circuit 29 and a switch changeover circuit 31. When the realizing resistance value is turned to an upper/lower limit in teh present connecting method of the MOSFET, according to the control signal of the bias voltage setting circuit 30 to change the realizing resistance value the switch changeover control circuit 31 switches the connecting state of the MOSFET to realize much larger or smaller resistance. Thus, since the state of connector the plural MOSFET is switched corresponding to the change of the realizing resistance value, the variable resistance value range of the MOSFET can be easily enlarged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable resistance circuit whose variable range can be expanded by an electrical control signal.

[Conventional technology]

An integratable variable resistor can be realized by switching resistors having a plurality of different resistance values. An example of this variable resistance circuit is shown in FIG.

In the figure, 1 is a resistor, 2 is an input terminal, 3 is an output terminal,
4 indicates a switch. The resistors R11R2, R:l of 1 are resistors having different resistance values, and different resistances are realized by switching these. When a variable resistance circuit using resistance switching is integrated, it has the disadvantage that the area becomes too large because it uses a plurality of resistors that occupy a large area on an IC chip.

MO in a variable resistance circuit that can be made into a 1-chip monolithic IC
There is an SFET resistance circuit. This MOSFET resistance circuit uses a MOSFET as a voltage-controlled resistance element that controls drain current using a gate-source voltage. MOSFET resistance circuit uses MOSFET as a resistor
This circuit is composed of a bias voltage setting circuit that determines the gate-source voltage of the MOSFET. Figure 2 shows the circuit configuration. In the same figure, 5-1 is an input terminal;
-2 is an output terminal, 6 is a MOSFET, and 7 is a bias voltage setting circuit.

There are two methods for correcting the resistance value using a bias voltage setting circuit: a direct control method and an indirect control method. - As an example, FIG. 3 shows a configuration using two MOSFETs using the direct control method. In the same figure, 8 is an input terminal, 9 is an output terminal, 1
0 to 19 are analog switches, 20 and 21 are MOSFE
T, 22 and 23 are bias voltage holding capacitors between the gate and source of the MOSFET, and 24 is a bias voltage setting circuit between the gate and source of the MOSFET. Analog switches IO-14 and 15-19 are simultaneously supplied with complementary clock signals whose logic "1" does not overlap.

In the first state, the MOSFET 20 is connected to the input terminal 8 and the output terminal 9 via the analog switches 10 and 12, and the drain, gate, and source of the MOSFET 21 are connected to the bias voltage setting circuit via the analog switches 11, 14, and 13, respectively. 24.

In the second state, MOSFET 21 is connected to input terminal 8 and output terminal 9 via analog switches 15 and 18, and the drain, gate, and source of MOSFET 20 are connected to the bias voltage setting circuit via analog switches 16, 17, and 19, respectively. 24. If you look at the resistance terminal, you can see a resistance that always has the same value even if the MOSFET is replaced. In this MOSFET variable resistance circuit,
For example, if the high potential side of the power supply voltage is 5■ and the low potential side is 0■, the range of bias voltage between the gate and source that is actually applied by the bias voltage setting circuit is 1.5V ~
It is about 3.5■. FIG. 4 shows the drain current characteristics with respect to the gate-source voltage of the MOSFET. MOS in the region showing the triode characteristics of MOSFET based on Figure 4
FIG. 5 shows the resistance value characteristics with respect to the gate-source voltage of the FET. The output range of the bias voltage setting circuit is ■□8
~ ■ If it is 1,7, the variable resistance range of MOSFET is RI
~R3.

[Problem to be solved by the invention]

In the above-mentioned conventional circuit, the power supply voltage is increased (by doing so, the variable gate-source voltage range can be expanded, but this is disadvantageous in terms of power consumption).

Therefore, under a constant power supply voltage, the range of variable gate-source voltage is limited, so MOSFET
The disadvantage is that the range of variable resistance values is limited.

The range of resistance values of the MOSFET variable resistance circuit is limited by the upper and lower limits of the output of the bias voltage setting circuit when a MOSFET of a certain size is used alone.

The upper and lower limits of the bias voltage setting circuit can be expanded by increasing the tBt pressure, but since it is advantageous to have a smaller power supply voltage especially when integrated, when a MOSFET variable resistor is made into a monolithic IC, the variable resistance value Expanding the range is difficult. In view of this problem, an object of the present invention is to obtain a MOSFET variable resistance circuit that can expand the variable range of filter frequency characteristics.

[Means to solve the problem]

The MOSFET variable resistance circuit of the present invention includes a bias voltage setting circuit that applies a required bias between the gate and source of the MOSFET, a plurality of MOSFETs as resistors,
A switch circuit that changes the connection form of MOSFET,
The bias voltage setting circuit includes a switch switching control circuit that controls the switch circuit using a control signal from the bias voltage setting circuit. What is the actual resistance value? When the upper or lower limit of the connection method of 105FI"T is reached, the switch changeover control circuit changes the MOSFET connection state to realize a larger or smaller resistance using the control signal of the bias voltage setting circuit that changes the realized resistance value. Switch.

Unlike conventional technology, the main feature is that the connection state of multiple MOSFETs can be switched according to changes in the realized resistance value.

〔Example〕

A feature of the present invention is that, compared to conventional MOSFET resistance circuits, a resistance circuit with a wider variable resistance value range can be realized by automatically switching the connection state of MOSFETs depending on the realized resistance value. A plurality of common MOSFET resistance circuits of the present invention? FIG. 1 shows a configuration for switching the connection state of the 105FET. In the figure, 25 is an input signal terminal, 26 is an output signal terminal, 33 is a clock signal input terminal, 27 and 28 are analog switches, 30 is a gate-source bias voltage setting circuit, and 29 is a MOS
A MOSFET switching circuit composed of a switch that changes the connection state of the FET and a plurality of MOSFETs as a resistor, 31 is a switch switching circuit that changes the connection state of the MOSFET switching circuit 29 by a control signal of a bias voltage setting circuit. show. The analog switches 2 and 2-1 connected to the resistance terminals of the MOSFET switching circuit are simultaneously driven by complementary lock signals with no overlapping logic until this logic rll becomes 0. Let T be the time. -1 and 2 to analog switch 2
+1 shifts the time at which the logic becomes "1" by T/n. '-1 to analog switch 2 connected to voltage setting circuit
becomes logic "1" only for T/n time immediately before the opposing analog switch 2k becomes logic "1". By this method, the MOSFET variable resistance circuit can realize n resistances. FIG. 7 shows a general diagram of a MOSFET switching circuit constituting a MOSFET variable resistance circuit. 37 is an input terminal, 36
is an output terminal, 35 is an input terminal from a gate-source bias voltage setting circuit, 34 is a control signal input terminal from a switch switching control circuit, 35 to 41 are analog switches, and 42 is a MOSFET. When m MOSFETs are used, only the m-th analog switch among the analog switches 40 has logic "L", the others have logic "0", and the analog switch 41 has logic "1" to "0" when correcting the resistance value.
Analog switches up to m number are logic "1", others are logic "0", and when a signal passes, analog switch 41
is logical "0". In addition, when the MOSFETs are connected in series, the analog switch 39 is set to logic "1" and the analog switch 38 is set to logic "0", and when the MOSFETs are connected in parallel, the analog switch 39 is set to logic "0", and the analog switch 38 is set to logic "0". 1”, m MOSFEs
T series and parallel connections can be realized.

As an example of a MOSFET resistance circuit, "IEE Transactions on Circuits and Systems, CAS-29, No. 5, 1982,
May (IEEE Transaction on C1
rcuits and Systems, vol, cA
s-29, No, 5. May, 1982. ) There is a switched resistor circuit using a switched capacitor integrator as a bias voltage setting circuit used in the switched resistor filter described in J. As an example of a case where the MOSFET variable resistance circuit of the present invention is applied to a switched resistor circuit, one MOSFET and two M
FIG. 8 shows a circuit configuration when correcting the resistance value when the connection state is changed to a series connection of OSFETs. In the same figure, 46
is an input terminal, 63 is an output terminal, 51 to 59 are analog switches, 60 and 61 are MOSFETs, 47 and 48 are capacitors that hold the bias voltage between the gate and source, 4
3 is a clock signal input terminal that controls the analog switch of the switched capacitor integrator, 45 is a frequency detector that detects the frequency of the clock signal, and 44 is used to select from one MOSFET to two MOSFETs based on the information from the frequency detector.
49 is a switching control circuit for changing the connection state of the series connection; 49 is a sampling capacitor of a switched capacitor integrator; 5
0 indicates an integral capacitance, and 60 indicates an operational amplifier. By simultaneously inputting complementary lock signals with no overlap of logic "1" to the analog switches 56 to 59, the analog switches 56 to 59 and the sampling capacitor C have an equivalent resistance value of
Realize R= 1/(rsc-c) 1). The resistance value of the MOSFET is corrected to be equal to this equivalent resistance value. Therefore, MOSFE
Is the realized resistance value Ror of T equal to RFE? = 1/Cr5c
-C) (2). FIG. 9 shows the time changes of the analog switches 51 to 55 with respect to the time change of the clock frequency of the analog switches of the pinched capacitor integrator, and the operation thereof will be explained. 2 MOSFETs
Assume that the same size is used. Single MOS
For FETs, the output voltage range of the bias voltage setting circuit y a
For i, ~■□, the variable resistance value range is R1□~Rt
If two MOSFETs are connected in series, the variable resistance range will be 2Rr*mx” R+m=n.If the realized resistance value is around R1,7, that is, if the clock frequency of the switched capacitor integrator is below ft, then By setting the analog switches 54 and 55 to logic "1" and setting the analog switches 51 to 53 to logic "o", one MOSFET type can be seen as a resistor between the input terminal 46 and the output terminal 63. When the realized resistance value increases and the realized resistance value Rt automatically sets the analog switches 54 and 55 to logic rQJ, and sets the analog switches 51 to 53 to logic "1", a resistance of 2 is output from the input terminal 46 and the output terminal 63. MOSF
Automatically change the connection state so that the ET series connection type is visible. By connecting two MOSFETs in series, a maximum resistance value of 2R, □ can be achieved. Therefore, MOSF
Automatically changes the ET connection method from one MOSFET type to two
2R1 by switching to MOSFET series connection type.
The variable resistance value range can be expanded to □ to Rl,...in. M
FIG. 10 shows the resistance value characteristics with respect to the gate-source voltage of the OSFET. By switching more MOSFETs, the variable resistance value range can be further expanded. As is clear from this result, there is an improvement over the conventional technology in that the resistance value range can be expanded.

〔Effect of the invention〕

The present invention automatically changes the connection state of multiple MOSFETs depending on the realized resistance value, thereby improving the connection state of multiple MOSFETs.
It has become possible to expand the variable resistance value range compared to the ET resistance circuit. In particular, is the resistance value determined by an electrical control signal from the control circuit inside the filter? Since the resistance value of the 'l05FET can be expanded, there is an advantage that monolithic integration is possible.

[Brief explanation of the drawing]

Figure 1 shows the circuit configuration of the MOSFET resistance circuit of the present invention, Figure 2 is a configuration diagram of a conventional MOSFET resistance circuit, Figure 3 is an example of a conventional directly controlled MOSFET resistance circuit, and Figure 4 shows the drain current of the MOSFET. Characteristics, Figure 5 is MOSF
ET gate-source voltage resistance characteristics, Fig. 6 is a configuration diagram of a variable resistance circuit using a conventional resistance combination, Fig. 7 is another circuit configuration of the MOSFET resistance circuit of the present invention, and Fig. 8 is a 1SFET resistor of the present invention. MOSFE in an example of a circuit
The circuit configuration when correcting the T resistance, FIG. 9 shows the MOSFET gate-source voltage resistance value characteristics, and FIG. 10 shows the resistance value characteristics with respect to the MOSFET gate-source voltage. 1...Resistance, 2, 5-1. 8.25.37.46...Input terminal,
3, 5-2. 9.26.36.63...output terminal,
4...Switch, ? , 24.30...bias voltage setting circuit, 6, 2
0.21.42.60.61-MOSFET, 22, 2
3.47.48... Capacitor, 10-19.27.
28.37-40.51-59... Analog switch, 45... Frequency detector, 31, 44... Switch switching control circuit, 29...?
105FET switching circuit, 62... operational amplifier, 33... clock signal input terminal, 34... control signal input terminal, 53... reference voltage input terminal, 35... gate voltage long sword terminal. Below 1 Figure 2 Figure 3 Figure 5 Figure 6 Figure 7 and Figure 8 Figure 9

Claims (1)

[Claims] MOSF where the area between the gate and drain is used as a resistor
In the ET resistance circuit, the MOSFET resistance circuit includes:
A plurality of MOSFETs (field effect transistors) as resistors, a bias voltage setting circuit that applies a required bias voltage between the gate and source of the MOSFET, a switch circuit that changes the connection form of the MOSFET, and the bias voltage A MOSFET resistance circuit comprising a switch switching control circuit that controls the analog switch using a control signal from a setting circuit.