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EL4083

Current Mode Four Quadrant Multiplier

Intersil 

EL4083

General Operating Information

IZ Input (Bias, Divisor) and Power Supplies

The IZ pin is a low impedance (< 20Ω) virtual ground current

input. It can accept positive current from a resistor

connected to a positive voltage source or the positive

supply. The instantaneous bias for the multiplier gain core is

proportional to this current value. Negative applied current

will put the multiplier portion of the circuit in a zero bias state

and the voltage at the pin will be clamped at a diode drop

below ground. The part will respond in a similar manner to

currents from a current source such as the output of a

transconductance amplifier or one of its own outputs. The

overall transfer equation for the EL4083 is:

K(IX × IY)/IZ = (IXY-IXY), K ~ 1

As can be seen from the equation, the Z input can serve as a

divisor input. However, it is different from the other two

inputs in that the value of its current determines the supply

current of the part and the bandwidth and compliance range

of the outputs and other two inputs. Table 1 gives the

equations describing these and other important

relationships. These dependencies can complicate and/or

limit the usefulness of this pin as a computational input. The

IZ dependence of the impedance of the multiplying inputs

can be particularly troublesome. See the IZ divider and the

RMS#2 circuit sections of the application note for some

ways of dealing with this.

The primary intended use for the Z input is as a

programming pin similar in function to those on

programmable op amps. This enables one to trade off power

consumption against bandwidth and settling time and allow

the part to function within its power dissipation rating over its

full operational supply range (±4.5V - ±16.5V). The E4083

has been designed to function well for IZ values in the range

of 200µA < IZ < 1.6mA which corresponds to IX and IY signal

bandwidths of about 50MHz to over 200MHz. Higher values

of IZ may cause problems at temperature extremes while

lower values down to zero will progressively degrade the

input referred D.C. offsets and reduce speed. Below about

50µA of bias current the internal servo amplifier loop which

maintains the IZ pin at ground will lose regulation and the

voltage at the pin will start to move negative (see Figure 10).

This is accompanied by a significant increase in input

impedance of the pin. Figure 11 shows the A.C. bandwidth

of the IZ input as a function of the D.C. value of IZ. Figures 6

and 7 show the bandwidth and 1% settling time of the

multiplying inputs, IX and IY, as functions of IZ.

TABLE 1. BASIC DESIGN EQUATIONS AND RELATIONSHIPS

Positive Supply Current

Negative Supply Current

Power Dissipation (See Figures 4 and 5)

Multiplying Input(s) Impedance

Multiplying Input(s) Clip Point

Multiplying Input(s) Full Scale Value

Multiplying Input Resistor Values

(In Terms of Peak Input Signal)

Full Scale Output (Single Ended)

Full Scale Output (Differential)

IZ (Bias) Input Voltage vs IZ

IS+ = 3.4mA + IZ × 26

IS- = 4.5mA + IZ × 27

PWR = (+VS - (-VS)) × (4mA + IZ × 26.5)

RZX = RZY = (32Ω) × 1.6mA/IZ

IX (clip) = IY (clip) = IZ × 2

IX (fs) = IY (fs)= IZ × 1.25 (nominal)

RX = VX (peak)/IX (fs)

RY = VY (peak)/IY (fs)

IXY = IXY = IX (fs) × IY (fs)/(IZ×2)

(IXY - IXY) = IX (fs) × IY (fs)/IZ

(See Figure 10)

IZ Signal Bandwidth vs IZ

IX, IY Signal Bandwidth vs IZ

(See Figure 11)

(See Figure 6)

IX, IY 1% Settling Time vs IZ

(See Figure 7)

7

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