J111-E3 Vishay, J111-E3 Datasheet

J111-E3

Manufacturer Part Number

J111-E3

Description

51K2069

Manufacturer

Vishay

Datasheet

1.J111-E3.pdf (6 pages)

Specifications of J111-E3

Breakdown Voltage Vbr

-55V

Zero Gate Voltage Drain Current Idss

20mA

Gate-source Cutoff Voltage Vgs(off) Max

-10V

Power Dissipation Pd

360mW

Operating Temperature Range

-55Â°C To +150Â°C

No. Of Pins

Rohs Compliant

Yes

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Introduction: The Nature of VCRs

A voltage-controlled resistor (VCR) may be defined as a

three-terminal variable resistor where the resistance val-

ue between two of the terminals is controlled by a voltage

potential applied to the third.

For a junction field-effect transistor (JFET) under certain

operating conditions, the resistance of the drain-source

channel is a function of the gate-source voltage alone and

the JFET will behave as an almost pure ohmic resistor.

Maximum drain-source current, I

sistance r

is equal to zero volts (V

creased (negatively for n-channel JFETs and positively

for p-channel), the resistance will also increase. When the

drain current is reduced to a point where the FET is no

longer conductive, the maximum resistance is reached.

The voltage at this point is referred to as the pinchoff or

cutoff voltage and is symbolized by V

the device functions as a voltage- controlled resistor.

Updates to this app note may be obtained via facsimile by calling Siliconix FaxBack, 1-408-970-5600. Please request FaxBack document #70598.

Siliconix

10-Mar-97

Ohmic Region

DS(on)

, will exist when the gate-source voltage

Region 1

= 0). If the gate voltage is in-

Current Saturation Region

DSS

Region 2

, and minimum re-

= V

GS(off)

. Thus

Figure 1 details typical operating characteristics of an n-

channel JFET. Most amplification or switching operations

of FETs occur in the constant-current (saturated) region,

shown as Region II. A close inspection of Region I (the un-

saturated or pre-pinchoff area) reveals that the effective

slope indicative of conductance across the channel from

drain-to-source is different for each value of gate-source

bias voltage. The slope is relatively constant over a range of

applied drain voltages, so long as the gate voltage is also

constant and the drain voltage is low.

Resistance Properties of FETs

The unique resistance-controlling properties of FETs can

be deduced from Figure 2, which is an expanded-scale

plot of the encircled area in the lower left-hand corner of

Figure 1. The output characteristics all pass through the

origin, near which they become almost straight lines so

that the incremental value of channel resistance, r

essentially the same as that of dc resistance, r

function of V

Figure 2 shows an extension of the operating characteris-

tics into the third quadrant for a typical n-channel JFET.

While such devices are normally operated with a positive

drain-source voltage, small negative values of V

possible. This is because the gate-channel PN junction

must be slightly forward-biased before any significant

amount of gate current flows. The slope of the V

line is equal to I

by the amount of voltage applied to the gate. Minimum

is dictated by the geometry of the FET. A device with a

channel of small cross-sectional area will exhibit a high

be chosen where design requirements indicate the need

for a low r

DS(on)

, usually expressed as r

and a low I

DS(on)

GS.

DSS

. Thus a FET with high I

= 1/r

DS(on)

. This value is controlled

, occurs at V

AN105

DSS

, and is a

= 0 and

should

bias

, is

are

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J111-E3 Summary of contents

Page 1

Introduction: The Nature of VCRs A voltage-controlled resistor (VCR) may be defined as a three-terminal variable resistor where the resistance val- ue between two of the terminals is controlled by a voltage potential applied to the third. For a junction ...

Page 2

AN105 –1 200 –2 –3.0 V –400 –200 –3.0 V 200 400 GS V (mV) DS –2.5 V –200 –1.5 V ...

Page 3

R Diode Cathode when Signal Diode Swings Negative Anode VCR – Figure 5. Simple Attenuator Circuit VCR Linearization VCR – ...

Page 4

AN105 Experimental Results Figures 8 and 9 show low voltage output characteristic curves for a typical Siliconix n-channel voltage-controlled resistor, VCR7N. Bias conditions are shown both with and without feedback. Figure 8 shows a two-volt peak-to-peak signal on the V ...

Page 5

Distortion resulting from changes in temperature is also minimized by the feedback resistor technique. On-resis- tance will change with temperature in an inverse manner to the behavior of FET drain current. Table 1 presents the result of VCR laboratory performance ...

Page 6

... Table 2: Popular JFETs for VCR Applications Range M/C – Hermetic DS(on) 20 – 60 100 – 600 4 k – *Approximate equivalents to VCR_N specifications OUT VCR Figure 15. Cascaded VCR Attenuator Plastic Thru Hole* VCR2N J111 VCR4N 2N5486 VCR7N PN4119A V OUT VCR – Suface Mount* SST111 SST5486 SST4119 Siliconix 10-Mar-97 ...

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