9

With the higher attenuation ratio, the multiplier sees a

smaller input amplitude and distorts less, however the higher

output gain reduces circuit bandwidth. As seen in the next

curves, the peak differential gain error is 0.47% for the

attenuation ratio of 1.5, but only 0.27% with the gain of 2

constants. To maintain bandwidth, an external op amp can

output by the attenuation ratio.

Sinewave Oscillators

Generating a stable, low distortion sinewave has long been a

difficult task. Because a linear oscillator’s output tends to

grow or diminish continuously, either a clipping circuit or

automatic gain control (AGC) is needed. Clipping circuits

generate severe distortion which needs subsequent filtering,

and AGCs can be complicated.

Here is the EL4451 used as an oscillator with simple AGC:

The oscillation frequency is set by the resonance of a series-

tuned circuit, which may be an L-C combination or a crystal.

At resonance, the series impedance of the tuned circuit

drops and its phase lag is 0°, so the EL4451 needs a gain

setting the maximum gain in the EL4451. At such high gain,

gain until a stable 0.5Vrms output is produced.

Using a 2MHz crystal, output distortion was -53dBc, or

0.22%. Sideband modulation was only 14Hz wide at -90dBc,

limited by the filter of the spectrum analyzer used.

The circuit works up to 30MHz. A parallel-tuned circuit can

replace the 510

Ω resistor and the 510Ω resistor moved in

place of the series-tuned element to allow grounding of the

tuned components.

Filters

The EL4451 can be connected to act as a voltage-variable

integrator as shown:

EL4451 Leveler Circuit

Attenuation Ratio = 1.5

EL4451 Leveler Circuit

Attenuation Ratio = 2

FIGURE 2. LOW-DISTORTION SINEWAVE OSCILLATOR

EL4451 CONNECTED AS VARIABLE INTEGRATOR

EL4451