The ac input voltage is applied to the diagonally opposite ends of the bridge. Pdf a voltage controlled resistor vcr using quasifloatinggate mosfets qfgmos suitable for low voltage applications is presented. The mosfet as a voltage controlled resistor example a mosfet l 1 m m, t ox 10 nm, v t 1 v and m n 300 cm 2 vsec is to be used as 50 w terminating resistor when applying a gatesource voltage, v gs 5 volt. This simple, powerful circuit produces output current in accordance with the sign and magnitude of the control voltage.
With the help of voltage divider created by the resistor r5 and series resistors r4, r7 voltage at the adj pin of lm317 is controlled. These voltage levels control the frequency of the internal voltagecontrolled oscillator figure 2. In particular it should exhibit a symmetric behaviour in the vicinity of the origin positivenegative current for positivenegative voltages. High current dc regulated power supply circuit with lm317 5. It can be used as a fixedfrequency or voltagecontrolled oscillator vco. The intersil x9511 is a push button controlled potentiometer that is ideal for push button controlled resistance trimming. Pdf the paper discusses an application of the field effected transistor fet as a voltage controlled resistance which can be done in undergraduate. Its applications can be found in telecommunications, electronics and measurements such as active rc filters with variable cutoff frequencies, controlled oscillators, variable gain amplifiers, voltage or current dividers, voltage or current to frequency. Jan 26, 2009 to prevent the resistance from ever going too low you could put a low valve high power resistor in series 0. The voltagecontrolled resistor vcr is widely used in analog signal processing.
For a junction fieldeffect transistor jfet under certain operating conditions, the resistance of the. The ltc6990 is part of the timerblox family of versatile silicon timing devices. Controlled current source an overview sciencedirect topics. If v gs is below v gs,off, isnt the jfet would be in off condition. A new cmos floating linear resistor circuit with a wide linearity range is proposed. A variablegain or voltagecontrolled amplifier is an electronic amplifier that varies its gain depending on a control voltage often abbreviated cv vcas have many applications, including audio level compression, synthesizers and amplitude modulation a crude example is a typical inverting opamp configuration with a lightdependent resistor ldr in the feedback loop. Frequency tx or rx range voltage tuning range linear tuning nonlinear tuning fig. D continuous voltage controlled resistance d high offisolation d high input impedance. Accordingly, the reader is cautioned to verify that data sheets are current before. Junction field effect transistor jfet the single channel junction fieldeffect transistor jfet is probably the simplest transistor available. In some applications it is required to control a digital potentiometer that has an i2c interface, with a continuously varying analog signal.
Vcrs are commonly used in the following electronics. The major advantages of fgmos based voltagecontrolled grounded resistor fgvcgr are simplicity, low total harmonic distortion thd, and low power consumption. In conclusion the device works as a voltage controlled resistor where the conductance or resistance of channel is a function of gate voltage. The x9511 is a resistor array composed of 31 resistive elements. It has been observed that a minimum drain current exists without gate voltage but an applied gate voltage changes the conductance of the channel region. While the value can be made to change for a set of simulations by using a parametric sweep to move through a fixed sequence of values, a voltagecontrolled resistor can be made to change dynamically during a simulation. As vgs approaches the pinchoff voltage, rds rapidly increases. Pdf voltage controlled resistor using quasifloatinggate. Simple control circuits for electronic ballast design author. The circuit presented offers linear control of the resistance with ten to one resistance variation and infinite resolution, and a usable resistance range of approximately 100. This circuit shows an epad mosfet inverter circuit connected as a voltage controlled. To prevent the resistance from ever going too low you could put a low valve high power resistor in series 0. D gain ranging capabilitywide range signal attenuation d no circuit interaction d simplified drive.
The two main characteristics of a resistor are its resistance, r, in ohms and its power rating, p, in watts. Simulation of a voltage controlled resistor mimicking the. The paper presents fgmos based voltagecontrolled resistor operating at supply voltage of 0. Voltage controlled silicon oscillator the ltc 6990 is a precision silicon oscillator with a programmable frequency range of 488hz to 2mhz. A mosfet l 1 mm, t ox 10 nm, v t 1 v and m n 300 cm 2 vsec is to be used as 50 w terminating resistor when applying a gatesource voltage, v gs 5 volt.
A jfetbased circuit for realizing a precision and linear floating voltagecontrolled resistance vcr is presented for use in analog multipliers and progr. Pdf realisation of linear voltagecontrolled resistance in floating. Click on the image below to download the pcb layout in printable pdf format a4 page. This helps lm317 regulate the output voltage and keep it constant at the desired level. Cmos floating resistors the currents of the transistors m5, m6 and m7 similarly, the biasing voltage v, can be obtained are equal and are given, respectively, by. A voltagecontrolled, linear, nongrounded resistor in cmos technology is presented.
A plurality of switches for example, mos devices 34 are coupled to selectively shunt around one or more of the resistors 32 so as to change the endtoend resistance value of the circuit 30. If the current is greater than 300ma the resistance should be. While the value can be made to change for a set of simulations by using a parametric sweep to move through a fixed sequence of values, a voltage controlled resistor can be made to change dynamically during a simulation. The temperature responsive resistor and the bipolar. We consider the use of a nchannel fet as a voltage controlled resistor where the resistance between the drain and source is controlled by the gatesource. A voltage controlled resistor vcr has been realized by two active devices. K5 is v vx vw2 56 g v2 vc vt 60 therefore, the resistor current is. The resistance, r, provides the required reduction in current or the desired drop in voltage. A voltagecontrolled resistor vcr is a threeterminal active device with one input port and two. Using an analog voltage to control a digital potentiometer. A fixed attenuation circuit is coupled to receive the variable source signal and output an attenuated variable source signal. The circuit has four diodes connected to form a bridge. Hi everyone, from the figure, its shown that jfet is configured as voltagecontrolled resistor. Im on the hunt for some sort of analog voltagecontrolled potentiometer.
In most circuits the value of a resistor is fixed during a simulation. The nature of vcrs a voltage controlled resistor vcr may be defined as a threeterminal variable resistor where the resistance value between two of the terminals is controlled by a voltage potential applied to the third. The output is referred to the output reference terminal pin 1 which is normally grounded. Mosfet as a voltage controlled resistor electrical. Modeling voltagecontrolled and temperaturedependent resistors. It is based on the conversion of the transconductance of the mosfet in. Place the voltmeter and measure the voltage across the first bulb. A1, biased by v in, drives current through r in this case 10. Electrical symbolselectrical symbols are used to represent various electrical and electronic devices in a schematic diagram of an electrical or electronic.
A new method is introduced for generating a precise large. This technical brief offers one simple way of making a vcr using ltspice. Grounded voltage controlled positive resistor with ultra low. The inputport voltage controls the value of the resistor between the output ports. Mike engelhardt has been writing physical simulators for 39 years. If the current through the resistor is less than 300ma then the resistance should be close to 0. Jfet as voltagecontrolled resistor all about circuits. The circuit employs 14 transistors all operating in the saturation region. Voltage controlled resistor using quasifloatinggate mosfets. A feedback voltage obtained from voltage divider r 1 and r 2 is applied to the opamps noninverting input and compared to the zener voltage to control the drive current to the transistor. Although theres no spice component that directly models this device, you can easily put one together. Modeling voltagecontrolled and temperaturedependent. The circuit has a bandwidth of 10 mhz, and the voltage across the resistance can be as large as 12 v.
If there is no tolerance band, then find the side that has. There are both floatingvoltage controlled resistors and grounded floating. A voltage controlled variable resistor circuit is configured to variably attenuate a variable source signal. The circuit 30 is implemented using a plurality of series connected resistors 32. Between each element and at either end are tap points accessible to the wiper element. In this work, a new cmos based grounded voltage controlled positive resistor gvcpr with one control voltage is proposed. In conclusion, the device works as a voltage controlled resistor vcr where the conductance or resistance of channel is a function of gate voltage. That is, the load current drainsource current of a fet is controlled by the voltage applied on the gate pin. Vcrs are most often built with fieldeffect transistors fets.
Intersil corporation reserves the right to make changes in circuit design andor specifications at any time without notice. Intersil semiconductor products are sold by description only. A voltage controlled resistor of the junction gate field effect type is temperature compensated by a circuit including the emitterbase junction of a bipolar transistor and also a temperature responsive resistor having a temperature sensitivity which is substantially the same as that of the channel of the voltage controlled resistor. Voltage controlled oscillators tuning a voltage controlled oscillator vco is an oscillator whose frequency can be varied by a voltage or current. A resistor voltage divider at the vco pin programs the desired vco voltage levels. Why are mosfets better than bjts in application of voltage. Jfet draintosource voltage variation to follow the development in your text, the first effect were going to look at is the variation of the draintosource voltage through the applied voltage v dd. In the ohmic region1, the draintosource current, i ds, depends on the gatetosource. The position of the wiper element is controlled by the pu and pd inputs. In this work, a new cmos based grounded voltage controlled positive. The vcr is one of the numerous interesting circuit elements that can be produced by using a jfet junction fieldeffect transistor with simple biasing. Technically the mosfet can operate as a variable resistor, but there are two main issues. An important aspect that students miss since it is not explicitly stated is that, on changing the voltage applied on the fets gate pin the resistance offered by.
Voltage controlled resistor using quasifloatinggate mosfets article pdf available in maejo international journal of science and technology 71. Fully integrated, 8channel voltage controlled amplifier. A voltagecontrolled resistor vcr may be defined as a threeterminal variable resistor where the resistance val ue between two of the terminals. D variable gain amplifiers d voltage controlled oscillator d agc description. A modified circuit which employs one more transistor, such that it is threshold voltage independent, is also given. A jfetbased circuit for realizing a precision and linear floating. It wont be very easy to tune it to behave like a proper resistor. A voltagecontrolled resistor in cmos technology using bisection of. The voltagecontrolled resistors, find applications in the area of analog signal processing such as filters,, dividers, amplifiers, and oscillators, etc.
One such function that has been difficult to find is a voltage. Precision wide range voltage and current regulator, mc1466l datasheet, mc1466l circuit, mc1466l data sheet. How to design an optimal electronic load for highcurrent. Model of voltage controlled voltage source amplifier opamp, vs is the input signal source, rs is the signal source output resistor, ri is the input resistor of the opamp, ro is the output resistor of the opamp, rl is the load resistor, and av is the amplification factor of the opamp.
Section 6 current, voltage, and resistance in parallel and. If the direction of input current i n is changed as shown in fig. Technology voltagecontrolled resistor device based on. The principle can be applied for controlling any device with an i2c interface using an analog voltage, and hence can be used in various applications. A voltage applied to the ref terminal will be summed with the output signal. Im aware of fets acting as voltagecontrolled resistors in their linear region, but the characteristic has too small of an operating window and is not as. Pdf fgmos based voltagecontrolled grounded resistor. The mosfet as a voltage controlled resistor example.
This can be used to null offset voltage as shown in figure 2. The field effect transistor as a voltage controlled resistor we consider the use of a nchannel fet as a voltage controlled resistor where the resistance between the drain and source is controlled by the gatesource voltage. An operational transconductance amplifier ota may be used to implement a voltage controlled resistor as shown in. The nature of vcrs a voltagecontrolled resistor vcr may be defined as a threeterminal variable resistor where the resistance value between two of the terminals is controlled by a voltage potential applied to the third. The wattage rating indicates the amount of power the resistor can safely dissipate as heat. The iv characteristics of a field effect transistor fet is often done as a routine experiment in the undergraduate physics and electronics laboratories. Nothing hectic here, a small explanation of the working principle of the circuit. The bridge rectifier is a circuit, which converts an ac voltage to dc voltage using both half cycles of the input ac voltage. Design of voltagecontrolled resistor based on jfet and its. The bridge rectifier circuit is shown in the following figure. Grounded voltage controlled positive resistor with ultra. In the ohmic region which is quite narrow, in terms of output voltage the linearity is poor, and it also depends on input voltage.
Resistive mirrorbased voltage controlled resistor with generalized. An op amp drives the gate of a power mosfet to establish a controlled voltage across a sense resistor. Fully integrated, 8channelvoltage controlled amplifier for ultrasound with passive cw mixer, 0. An mos transistor operating below saturation region can implement a voltage controlled resistor vcr but with a limited range. Field effect transistors jfets or mosfets operating in both the ohmic and. Power mosfet as a voltage controlled resistor physics forums. In local oscillator applications, the vco frequency must be able to be varied over the rx or tx range quickly. A common request from spice users is a voltagecontrolled resistor.
Us3715609a temperature compensation of voltage controlled. The current through resistor r s is thus controlled to drop a voltage across r s so that the output voltage is maintained. Pdf voltage controlled resistor using quasifloating. From, it can be seen that the proposed circuit behaves as voltagecontrolled resistor and the control voltage v c controls the resistance value. Siliconix note an105 has some example circuits with jfets voltage control resistors. Im trying to draw out the schematic for a current controlled resistor that behaves as follows. Calculate the onresistance of an nmos transistor for v gs 2vand gs 5v if v tn 1vand k n 250 av2. Voltage controlled resistor advanced linear devices. A voltagecontrolled resistor redgarden engineering llc. This results in a controlled load current that flows.
Furthermore, the same textbook says that fet voltagecontrolled atenuators were commonly used as automatic gain control devices dynamic range compression for example by dolby. A voltagecontrolled resistor vcr is a threeterminal device that varies the resistance between two terminals relative to voltage in the third terminal. Hey all, im on the hunt for some sort of analog voltage controlled potentiometer. Fully integrated, 8channel voltage controlled amplifier for. There are many functions included within the free download of the software and available on.
Realisation of linear voltagecontrolled resistance in floating form. A voltage controlled resistor vcr is a threeterminal active device with one input port and two output ports. Motorola, alldatasheet, datasheet, datasheet search site for electronic components and semiconductors, integrated circuits, diodes, triacs, and other semiconductors. Ideally, something that has a 0 5v input swing with a linear resistance output from 0 10kohms, respectively.
The figure to the right is a modified version of figure 6. The voltmeter is always placed in parallel with the resistor light bulb. Placing an ammeter in the circuit to measure the current through a light bulb is similar to placing a switch next to the bulb to control it. If such a device should be able to act as a voltagecontrolled resistor it should have a voltagecurrent characteristic that is at least similar to an ohmic resistor. The vcr2n4n7n jfet voltage controlled resistors have an ac drainsource resistance that is controlled a dc bias voltage vgs applied to their high impedance gate terminal. A voltage controlled amplifier can be realised by first creating a voltage controlled resistor vcr, which is used to set the amplifier gain. Pspice simulations taking into account the second order effects due to the channel length modulation and mobility. The resistance of a mosfet operated in the linear mode is given by. If the current is greater than 300ma the resistance should be 2ohm. A voltagecontrolled resistor vcr is a threeterminal active device with one input port and two output ports.
Simple control circuits for electronic ballast design. An important aspect that students miss since it is not explicitly stated is that, on changing the voltage applied on the fets gate pin the resistance offered by the fets channel changes. For a jfet to be effective as a linearly responding resistor, why its important to limit v ds to a value that is small compared with v gs,off and to keep v gs below vgs,off. Electrical symbols for android free download and software. Vca5807 1features description 8channelvoltage controlled amplifier the vca5807 is an integrated voltage controlled amplifier vca specifically designed for ultrasound. The field effect transistor as a voltage controlled resistor. Precision unity gain differential amplifier datasheet. There are many functions included within the free download of the software and available on the internet.
1289 1045 110 965 1308 12 837 1207 9 382 201 289 569 1554 410 1285 9 1324 1004 1085 621 1297 1182 1375 432 1242 352 395 1476 1062 325 297 60