XR2206CP datasheet(11/16 Pages) EXAR

11 / 16 page

XR-2206

Rev. 1.03

With External Adjustment:

The harmonic content of sinusoidal output can be

reduced to -0.5% by additional adjustments as shown in

Figure 12.

The

potentiometer,

RA,

adjusts

the

sine-shaping

resistor,

and

RB provides the fine

adjustment for the waveform symmetry. The adjustment

procedure is as follows:

Set RB at midpoint and adjust RA for minimum

distortion.

With RA set as above, adjust RB to further reduce

distortion.

Triangle Wave Generation

The circuits of

Figure 11 and Figure 12 can be converted

to triangle wave generation, by simply open-circuiting Pin

13 and 14 (i.e., S1 open). Amplitude of the triangle is

approximately twice the sine wave output.

FSK Generation

Figure 13 shows the circuit connection for sinusoidal FSK

signal operation. Mark and space frequencies can be

independently adjusted by the choice of timing resistors,

R1 and R2; the output is phase-continuous during

transitions. The keying signal is applied to Pin 9. The

circuit can be converted to split-supply operation by

simply replacing ground with V-.

Pulse and Ramp Generation

Figure 14 shows the circuit for pulse and ramp waveform

generation. In this mode of operation, the FSK keying

terminal (Pin 9) is shorted to the square-wave output (Pin

11), and the circuit automatically frequency-shift keys

itself between two separate frequencies during the

positive-going and negative-going output waveforms.

The pulse width and duty cycle can be adjusted from 1%

to 99% by the choice of R1 and R2. The values of R1 and

R2 should be in the range of 1kW to 2MW.

PRINCIPLES OF OPERATION

Description of Controls

Frequency of Operation:

The frequency of oscillation, fo, is determined by the

external timing capacitor, C, across Pin 5 and 6, and by

the timing resistor, R, connected to either Pin 7 or 8. The

frequency is given as:

+ 1

and can be adjusted by varying either R or C. The

recommended values of R, for a given frequency range,

as shown in

Figure 5. Temperature stability is optimum

for 4k

W < R < 200kW. Recommended values of C are from

1000pF to 100

mF.

Frequency Sweep and Modulation:

Frequency of oscillation is proportional to the total timing

current, IT, drawn from Pin 7 or 8:

320

T (mA)

mF)

Timing terminals (Pin 7 or 8) are low-impedance points,

and are internally biased at +3V, with respect to Pin 12.

Frequency varies linearly with IT, over a wide range of

current values, from 1

mA to 3mA. The frequency can be

controlled by applying a control voltage, VC, to the

activated timing pin as shown in

Figure 10. The frequency

of oscillation is related to VC as:

+ 1

) R

–

where VC is in volts. The voltage-to-frequency conversion

gain, K, is given as:

+ f V

C + –

0.32

Hz V

CAUTION: For safety operation of the circuit, IT should be

limited to

3mA.

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