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EL4083

Current Mode Four Quadrant Multiplier

Intersil 

EL4083

IX and IY (Multiplier) Inputs and Offset Trimming

The IX and IY pins are low impedance (IZ dependent) virtual

ground current inputs that accept bipolar signals. The input

referred clip value is equal to IZ × 2 while the full scale value

has been chosen to be 1.25 × IZ to maintain excellent distortion

and linearity performance. Operating at higher full scale values

will degrade these two parameters and, to some extent,

bandwidth while improving the signal to noise performance,

feedthrough and control range.

The EL4083 is fundamentally different from conventional

voltage mode multipliers in that the available input range can

be tailored to accommodate voltage sources of almost any size

by selecting appropriate input series resistor values. If desired,

one can interface with voltages that are much greater than the

supplies from which the part is powered. Current source signals

can be connected directly to the multiplier inputs. The parts’

dynamic range can also be tailored to a large extent for a

current signal by the appropriate selection of IZ. These inputs

act in the same manner as a virtual ground input of an

operational amplifier and thus can serve as a summing node for

any number of voltage and/or current signals. Outputs of

components such as current output DACs, transconductance

amplifiers and current conveyors can be directly connected to

the inputs.

Ideally, a multiplier should give zero output if either one of its

multiplying inputs is zero. A nonzero output under these

conditions is caused by a combination of input and output

referred offsets. An output referred offset can be thought of as

a fixed value added to the output and thus only affects D.C.

accuracy. An input referred offset at a multiplying input allows

signal to feedthrough from the other multiplying input to the

output(s). The EL4083 is trimmed during testing at Elantec for

X and Y input referred offset for IZ = 1.6 mA. The internal trim

networks provide a current to each input which nulls the

feedthrough caused by internal device mismatches. These

current values are ratioed to the value of IZ so that the input

referred nulls are largely maintained at different values of IZ.

However, there will be some mistracking in the trim networks so

that the input referred null point will deviate away from zero at

values of IZ lower than 1.6mA. Figure 9 shows optional external

input and output referred offset trim networks which can be

used as needed to improve performance.

As mentioned, the output referred offset only affects D.C.

accuracy which may not be an issue in A.C. applications. In

gain control applications one may only need to null feedthrough

with respect to the gain control input.

In gain control (VCA) applications the X input should be used

as the control input and the signal applied to the Y input since it

has slightly higher bandwidth and better linearity and distortion

performance.

Current Outputs (IXY, IXY), Feedthrough and

Distortion

Another unique feature of the EL4083 is the differential ground

referenced current output structure. These outputs can drive

50Ω terminated lines and reactive loads such as transformers,

baluns, and LC tank and filter circuits directly (See EL2082

Data Sheet_Receiver IF Amplifier (Figure 19). The EL2082 also

has a current output.). Unlike low impedance follower buffers,

these outputs do not interact with the load to produce ringing or

instability. If a high level low impedance output is required, the

outputs can be recovered differentially and converted to a

single ended output with a fast op amp such as the EL2075

(see Figure 19). The outputs can also drive current input

devices such as CMF amps, current conveyors and its own

inputs directly by simple connection.

Figures 12 and 14 show the nulled gain and feedthrough

characteristics of the IXY and IXY outputs which are virtually

identical and differ only in phase. Figure 12 is with the A.C.

signal applied to the X input with Y used as the gain control and

in Figure 14 these signals are reversed. Note that in both cases

the signal feedthrough rolls up and peaks near the cutoff

frequency. This is quite typical of the performance of all

previous four quadrant multipliers. Figures 13 and 15 show the

corresponding gain/feedthrough characteristics for the

differentially recovered output signal IXY-IXY. Note that in this

case the peak feedthrough at high frequencies is lower by more

than 40dB (See EL2082 Data Sheet - Receiver IF Amplifier

[Figure 19]. The EL2082 also has a current output).

General Operating Information

Figures 16 and 17 show the total harmonic distortion for the

single-ended and differential recovered outputs for a full scale

A.C. input signal on one input and a full scale D.C. control

signal on the other. Note that above about one megahertz to

the cutoff frequency the THD of the differentially recovered

signal is as much as 10dB lower than the single-ended signals.

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