EL4450CM 데이터 시트보기 (PDF) - Intersil

부품명

상세내역

제조사

EL4450CM

Wideband Four-Quadrant Multiplier

Intersil 

EL4450

Applications Information

The EL4450 is a complete four-quadrant multiplier with

90MHz bandwidth. It has three sets of inputs; a differential

multiplying X-input, a differential multiplying Y-input, and

another differential input which is used to complete a

feedback loop with the output. Here is a typical connection:

The gain of the feedback divider is H, and

H = RG/(RG + RF). The transfer function of the part is:

VOUT = AO × (1/2 × ((VINX+–VINX-) × (VINY+–VINY-)) +

(VREF–VFB)).

VFB is connected to VOUT through a feedback network, so

VFB = H*VOUT. AO is the open-loop gain of the amplifier, and

is about 600. The large value of AO drives:

(1/2 × ((VINX+–VINX-) × (VINY+–VINY-)) + (VREF–

VFB))→0.

Rearranging and substituting for VREF:

VOUT = (1/2 × ((VINX+–VINX-) × (VINY+–VINY-))

+VREF)/H, or VOUT = (XY/2 + VREF)/H

Thus the output is equal to one-half the product of X and Y

inputs and offset by VREF, all gained up by the feedback

divider ratio. The EL4450 is stable for a direct connection

between VOUT and FB, and the feedback divider may be

used for higher output gain, although with the traditional loss

of bandwidth.

It is important to keep the feedback divider’s impedance at

the FB terminal low so that stray capacitance does not

diminish the loop’s phase margin. The pole caused by the

parallel impedance of the feedback resistors and stray

capacitance should be at least 150MHz; typical strays of 3pF

thus require a feedback impedance of 360Ω or less.

Alternatively, a small capacitor across RF can be used to

create more of a frequency-compensated divider. The value

of the capacitor should scale with the parasitic capacitance

at the FB input. It is also practical to place small capacitors

across both the feedback resistors (whose values maintain

the desired gain) to swamp out parasitics. For instance, two

10pF capacitors across equal divider resistors for a

maximum gain of 1 will dominate parasitic effects and allow

a higher divider resistance.

The REF pin can be used as the output’s ground reference,

or for DC offsetting of the output, or it can be used to sum in

another signal.

Input Connections

The input transistors can be driven from resistive and

capacitive sources, but are capable of oscillation when

presented with an inductive input. It takes about 80nH of

series inductance to make the inputs actually oscillate,

equivalent to four inches of unshielded wiring or about 6 of

unterminated input transmission line. The oscillation has a

characteristic frequency of 500MHz. Placing one’s finger (via

6

a metal probe) or an oscilloscope probe on the input will kill

the oscillation. Normal high-frequency construction obviates

any such problems, where the input source is reasonably

close to the input. If this is not possible, one can insert series

resistors of around to 51Ω to de-Q the inputs.

Signal Amplitudes

Signal input common-mode voltage must be between (V-)

+2.5V and (V+) -2.5V to ensure linearity. Additionally, the

differential voltage on any input stage must be limited to ±6V

to prevent damage. The differential signal range is ±2V in the

EL4450. The input range is substantially constant with

temperature.

The Ground Pin

The ground pin draws only 6µA maximum DC current, and

may be biased anywhere between (V-) +2.5V and (V+)

-3.5V. The ground pin is connected to the IC’s substrate and

frequency compensation components. It serves as a shield

within the IC and enhances input stage CMRR over

frequency, and if connected to a potential other than ground,

it must be bypassed.

Power Supplies

The EL4450 works well on supplies from ±3V to ±15V. The

supplies may be of different voltages as long as the

requirements of the GND pin are observed (see the Ground

Pin section for a discussion). The supplies should be

bypassed close to the device with short leads. 4.7µF

tantalum capacitors are very good, and no smaller bypasses

need be placed in parallel. Capacitors as low as 0.01µF can

be used if small load currents flow.

Single-polarity supplies, such as +12V with +5V can be

used, where the ground pin is connected to +5V and V- to

ground. The inputs and outputs will have to have their levels

shifted above ground to accommodate the lack of negative

supply.

The power dissipation of the EL4450 increases with power

supply voltage, and this must be compatible with the

package chosen. This is a close estimate for the dissipation

of a circuit:

PD =2*IS,max*VS + (VS–VO)*VO/RPAR

where

IS,max is the maximum supply current

VS is the ± supply voltage (assumed equal)

VO is the output voltage

RPAR is the parallel of all resistors loading the output

For instance, the EL4450 draws a maximum of 18mA. With

light loading, RPAR→∞ and the dissipation with ±5V supplies

is 180mW. The maximum supply voltage that the device can

run on for a given PD and the other parameters is:

VS,max = (PD + VO2/RPAR)/(2IS + VO/RPAR)

Share Link: