Semiconductor IL0 September 99 File Number 64. Precision Waveform Generator/Voltage ontrolled Oscillator The IL0 waveform generator is a monolithic integrated circuit capable of producing high accuracy sine, square, triangular, sawtooth and pulse waveforms with a minimum of external components. The frequency (or repetition rate) can be selected externally from 0.00Hz to more than 00kHz using either resistors or capacitors, and frequency modulation and sweeping can be accomplished with an external voltage. The IL0 is fabricated with advanced monolithic technology, using Schottky barrier diodes and thin film resistors, and the output is stable over a wide range of temperature and supply variations. These devices may be interfaced with phase locked loop circuitry to reduce temperature drift to less than 50ppm/ o. Features Low Frequency Drift with Temperature.......50ppm/ o Low Distortion................ % (Sine Wave Output) High Linearity........... 0.% (Triangle Wave Output) Wide Frequency Range........... 0.00Hz to 00kHz Variable Duty ycle..................... % to 9% High Level Outputs...................... TTL to V Simultaneous Sine, Square, and Triangle Wave Outputs Easy to Use - Just a Handful of External omponents Required Ordering Information PART NUMBER STABILITY TEMP. RANGE ( o ) PAKAGE PKG. NO. IL0PD 50ppm/ o (Typ) 0 to 0 4 Ld PDIP E4. IL0JD 50ppm/ o (Typ) 0 to 0 4 Ld ERDIP F4. IL0BJD 0ppm/ o (Typ) 0 to 0 4 Ld ERDIP F4. IL0AJD 0ppm/ o (Typ) 0 to 0 4 Ld ERDIP F4. Pinout Functional Diagram SINE WAVE ADJUST SINE WAVE OUT TRIANGLE OUT IL0 (PDIP, ERDIP) TOP VIEW 4 N N SINE WAVE ADJUST URRENT SOURE # I I OMPARATOR # OMPARATOR # 6 DUTY YLE FREQUENY ADJUST FM BIAS 4 5 6 9 V- OR GND TIMING APAITOR SQUARE WAVE OUT FM SWEEP INPUT URRENT SOURE # BUFFER FLIP-FLOP BUFFER SINE ONVERTER V- OR GND 9 AUTION: These devices are sensitive to electrostatic discharge; follow proper I Handling Procedures. opyright Harris orporation 99
IL0 Absolute Maximum Ratings Supply Voltage (V- to ).............................. 6V Input Voltage (Any Pin)............................ V- to Input urrent (Pins 4 and 5)........................... 5mA Output Sink urrent (Pins and 9)..................... 5mA Operating onditions Temperature Range IL0A, IL0B, IL0............ 0 o to 0 o Thermal Information Thermal Resistance (Typical, Note ) θ JA ( o /W) θ J ( o /W) ERDIP Package................. 5 0 PDIP Package................... 5 N/A Maximum Junction Temperature (eramic Package)........5 o Maximum Junction Temperature (Plastic Package)........50 o Maximum Storage Temperature Range.......... -65 o to 50 o Maximum Lead Temperature (Soldering s)............ 00 o Die haracteristics Back Side Potential.................................... V- AUTION: Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. NOTE:. θ JA is measured with the component mounted on an evaluation P board in free air. Electrical Specifications V SUPPLY = ±V or +0V, T A = 5 o, R L = kω, Test ircuit Unless Otherwise Specified PARAMETER SYMBOL TEST ONDITIONS IL0 IL0B IL0A MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS Supply Voltage Operating Range V SUPPLY Single Supply + - +0 + - +0 + - +0 V, V- Dual Supplies ±5 - ±5 ±5 - ±5 ±5 - ±5 V Supply urrent I SUPPLY V SUPPLY = ±V (Note ) 0-0 - 0 ma FREQUENY HARATERISTIS (All Waveforms) Max. Frequency of Oscillation f MAX 0 - - 0 - - 0 - - khz Sweep Frequency of FM Input f SWEEP - - - - - - khz Sweep FM Range (Note ) - 5: - - 5: - - 5: - FM Linearity : Ratio - 0.5 - - 0. - - 0. - % Frequency Drift with Temperature (Note 5) f/ T 0 o to 0 o - 50 - - 0 - - 0 ppm/ o Frequency Drift with Supply Voltage f/ V Over Supply Voltage Range - 0.05 - - 0.05-0.05 - %/V OUTPUT HARATERISTIS Square Wave Leakage urrent I OLK V 9 = 0V - - - - - - µa Saturation Voltage V SAT I SINK = ma - 0. 0.5-0. 0.4-0. 0.4 V Rise Time t R R L = 4.kΩ - 0 - - 0 - - 0 - ns Fall Time t F R L = 4.kΩ - 40 - - 40 - - 40 - ns Typical Duty ycle Adjust (Note 6) D 9-9 - 9 % Triangle/Sawtooth/Ramp - Amplitude V TRIAN- GLE R TRI = 0kΩ 0.0 0. - 0.0 0. - 0.0 0. - xv SUPPLY Linearity - 0. - - 0.05 - - 0.05 - % Output Impedance Z OUT I OUT = 5mA - 00 - - 00 - - 00 - Ω
IL0 Electrical Specifications V SUPPLY = ±V or +0V, T A = 5 o, R L = kω, Test ircuit Unless Otherwise Specified (ontinued) PARAMETER SYMBOL TEST ONDITIONS IL0 IL0B IL0A MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS Sine Wave Amplitude V SINE R SINE = 0kΩ 0. 0. - 0. 0. - 0. 0. - xv SUPPLY THD THD R S = MΩ (Note 4) -.0 5 -.5 -.0.5 % THD Adjusted THD Use Figure 4 -.5 - -.0 - - 0. - % NOTES:. and currents not included.. V SUPPLY = 0V; and = kω, f khz nominal; can be extended 00 to. See Figures 5A and 5B. 4. kω connected between pins and, Triangle Duty ycle set at 50%. (Use and.) 5. Figure, pins and connected, V SUPPLY = ±V. See Typical urves for T.. vs V SUPPLY. 6. Not tested, typical value for design purposes only. Test onditions PARAMETER R L SW MEASURE Supply urrent kω kω kω.nf losed urrent Into Pin 6 Sweep FM Range (Note ) kω kω kω.nf Open Frequency at Pin 9 Frequency Drift with Temperature kω kω kω.nf losed Frequency at Pin Frequency Drift with Supply Voltage (Note ) kω kω kω.nf losed Frequency at Pin 9 Output Amplitude (Note ) Sine kω kω kω.nf losed Pk-Pk Output at Pin Triangle kω kω kω.nf losed Pk-Pk Output at Pin Leakage urrent (Off) (Note 9) kω kω.nf losed urrent into Pin 9 Saturation Voltage (On) (Note 9) kω kω.nf losed Output (Low) at Pin 9 Rise and Fall Times (Note ) kω kω 4.kΩ.nF losed Waveform at Pin 9 Duty ycle Adjust (Note ) Max 50kΩ ~.6kΩ kω.nf losed Waveform at Pin 9 Min ~5kΩ 50kΩ kω.nf losed Waveform at Pin 9 Triangle Waveform Linearity kω kω kω.nf losed Waveform at Pin Total Harmonic Distortion kω kω kω.nf losed Waveform at Pin NOTES:. The hi and lo frequencies can be obtained by connecting pin to pin (f HI ) and then connecting pin to pin 6 (f LO ). Otherwise apply Sweep Voltage at pin ( / V SUPPLY +V) V SWEEP V SUPPLY where V SUPPLY is the total supply voltage. In Figure 5B, pin should vary between 5.V and V with respect to ground.. V 0V, or ±5V V SUPPLY ±5V. 9. Oscillation can be halted by forcing pin to +5V or -5V.. Output Amplitude is tested under static conditions by forcing pin to 5V then to -5V.. Not tested; for design purposes only.
IL0 Test ircuit K K R L K +V 4 5 6 9 SW N.. IL0 R TRI 00pF K R SINE -V FIGURE. TEST IRUIT Detailed Schematic URRENT SOURES 6 R 0K Q Q Q Q 4 Q R K R Q 9K 6 9 Q 0 Q 4 Q R 0 Q Q R.K R 46 40K Q 5 Q 4 Q Q 5 Q Q 9 Q Q Q 6 R EXT B 5 4 R 4 0 R 60 R 6.K R 4 K R 5 40 Q 9 R 5 0 FLIP-FLOP R EXT A Q Q R 6 0 Q Q Q 4 EXT R 4.K R 4.K 5K R 4 4K OMPARATOR Q 5 Q Q6 Q Q 0 Q Q 9 Q Q R 4 K Q 5 Q6 Q Q40 R 4 K R 4 K K R 5K R 9 5K R 5K Q9 R 44 K BUFFEMPLIFIER R 9 00 Q 45 R 0 Q 44.K Q R 4 Q 4 K Q 4 R 5 R 6 K K R K Q 49 R Q 50 K Q 5 R.K R 4 00 Q 5 R 9 K Q 5 Q 54 SINE ONVERTER Q 46 Q 4 R K R 0 K Q 55 Q 4 Q 56 R 45 K R K R 5.K R 00 R 4 5 R 5 0 R 6 600 R 0 R 5 R 9 00 R 40 5.6K R EXT K Application Information (See Functional Diagram) An external capacitor is charged and discharged by two current sources. urrent source # is switched on and off by a flip-flop, while current source # is on continuously. Assuming that the flip-flop is in a state such that current source # is off, and the capacitor is charged with a current I, the voltage across the capacitor rises linearly with time. When this voltage reaches the level of comparator # (set at / of the supply voltage), the flip-flop is triggered, changes states, and releases current source #. This current source normally carries a current I, thus the capacitor is discharged with a net-current I and the voltage across it drops linearly with time. When it has reached the level of comparator # (set at / of the supply voltage), the flip-flop is triggered into its original state and the cycle starts again. Four waveforms are readily obtainable from this basic generator circuit. With the current sources set at I and I respectively, the charge and discharge times are equal. Thus a triangle waveform is created across the capacitor and the flip-flop produces a square wave. Both waveforms are fed to buffer stages and are available at pins and 9. 4
IL0 The levels of the current sources can, however, be selected over a wide range with two external resistors. Therefore, with the two currents set at values different from I and I, an asymmetrical sawtooth appears at Terminal and pulses with a duty cycle from less than % to greater than 99% are available at Terminal 9. The sine wave is created by feeding the triangle wave into a nonlinear network (sine converter). This network provides a decreasing shunt impedance as the potential of the triangle moves toward the two extremes. Waveform Timing The symmetry of all waveforms can be adjusted with the external timing resistors. Two possible ways to accomplish this are shown in Figure. Best results are obtained by keeping the timing resistors and separate (A). controls the rising portion of the triangle and sine wave and the state of the square wave. The magnitude of the triangle waveform is set at / V SUPPLY ; therefore the rising portion of the triangle is, t V / V SUPPLY = ------------- = ------------------------------------------------------------------ = ----------------- I 0. V SUPPLY 0.66 The falling portion of the triangle and sine wave and the 0 state of the square wave is: V /V R R SUPPLY A B t = ------------ = ----------------------------------------------------------------------------------- ( 0.) V = ------------------------------------- V SUPPLY SUPPLY 0.66( R ----------------------- 0.----------------------- A R B ) R A Thus a 50% duty cycle is achieved when =. If the duty cycle is to be varied over a small range about 50% only, the connection shown in Figure B is slightly more convenient. A kω potentiometer may not allow the duty cycle to be adjusted through 50% on all devices. If a 50% duty cycle is required, a kω or 5kΩ potentiometer should be used. With two separate timing resistors, the frequency is given by: f = --------------- = ------------------------------------------------------ t + t ------------ + ------------------------- 0.66 or, if = = R 0. f = ---------- (for Figure A) R FIGURE A. SQUARE WAVE DUTY YLE - 50% FIGURE B. SQUARE WAVE DUTY YLE - 0% FIGURE. PHASE RELATIONSHIP OF WAVEFORMS R L kω R L 4 5 6 9 4 5 6 9 IL0 IL0 K 0K V- OR GND FIGURE A. FIGURE B. FIGURE. POSSIBLE ONNETIONS FOR THE EXTERNAL TIMING RESISTORS V- OR GND 5
IL0 Neither time nor frequency are dependent on supply voltage, even though none of the voltages are regulated inside the integrated circuit. This is due to the fact that both currents and thresholds are direct, linear functions of the supply voltage and thus their effects cancel. Reducing Distortion To minimize sine wave distortion the kω resistor between pins and is best made variable. With this arrangement distortion of less than % is achievable. To reduce this even further, two potentiometers can be connected as shown in Figure 4; this configuration allows a typical reduction of sine wave distortion close to 0.5%. 4 5 6 9 kω IL0 0kΩ Selecting, and For any given output frequency, there is a wide range of R combinations that will work, however certain constraints are placed upon the magnitude of the charging current for optimum performance. At the low end, currents of less than µa are undesirable because circuit leakages will contribute significant errors at high temperatures. At higher currents (I > 5mA), transistor betas and saturation voltages will contribute increasingly larger errors. Optimum performance will, therefore, be obtained with charging currents of µa to ma. If pins and are shorted together, the magnitude of the charging current due to can be calculated from: R L 0kΩ kω kω V- OR GND FIGURE 4. ONNETION TO AHIEVE MINIMUM SINE WAVE DISTORTION R ( V-) 0.( V-) I = --------------------------------------- ------- = ----------------------------------- ( R + R ) R and R are shown in the Detailed Schematic. A similar calculation holds for. The capacitor value should be chosen at the upper end of its possible range. Waveform Out Level ontrol and Power Supplies The waveform generator can be operated either from a single power supply (V to 0V) or a dual power supply (±5V to ±5V). With a single power supply the average levels of the triangle and sine wave are at exactly one-half of the supply voltage, while the square wave alternates between and ground. A split power supply has the advantage that all waveforms move symmetrically about ground. The square wave output is not committed. A load resistor can be connected to a different power supply, as long as the applied voltage remains within the breakdown capability of the waveform generator (0V). In this way, the square wave output can be made TTL compatible (load resistor connected to +5V) while the waveform generator itself is powered from a much higher voltage. Frequency Modulation and Sweeping The frequency of the waveform generator is a direct function of the D voltage at Terminal (measured from ). By altering this voltage, frequency modulation is performed. For small deviations (e.g. ±%) the modulating signal can be applied directly to pin, merely providing D decoupling with a capacitor as shown in Figure 5A. An external resistor between pins and is not necessary, but it can be used to increase input impedance from about kω (pins and connected together), to about (R + kω). For larger FM deviations or for frequency sweeping, the modulating signal is applied between the positive supply voltage and pin (Figure 5B). In this way the entire bias for the current sources is created by the modulating signal, and a very large (e.g. 00:) sweep range is created (f = 0 at V SWEEP = 0). are must be taken, however, to regulate the supply voltage; in this configuration the charge current is no longer a function of the supply voltage (yet the trigger thresholds still are) and thus the frequency becomes dependent on the supply voltage. The potential on Pin may be swept down from by ( / V SUPPLY - V). 6
IL0 4 5 6 9 R L With a dual supply voltage the external capacitor on Pin can be shorted to ground to halt the IL0 oscillation. Figure shows a FET switch, diode ANDed with an input strobe signal to allow the output to always start on the same slope. R IL0 5K FM 4 5 9 K V- OR GND IL0 N94 FIGURE 5A. ONNETIONS FOR FREQUENY MODULATION N94 SWEEP VOLTAGE 4 5 6 9 R L N49-5V 0K OFF ON STROBE +5V (+V) -5V (-V) FIGURE. STROBE TONE BURST GENERATOR Typical Applications IL0 K The sine wave output has a relatively high output impedance (kω Typ). The circuit of Figure 6 provides buffering, gain and amplitude adjustment. A simple op amp follower could also be used. V- OR GND FIGURE 5B. ONNETIONS FOR FREQUENY SWEEP FIGURE 5. To obtain a 00: Sweep Range on the IL0 the voltage across external resistors and must decrease to nearly zero. This requires that the highest voltage on control Pin exceed the voltage at the top of and by a few hundred mv. The ircuit of Figure achieves this by using a diode to lower the effective supply voltage on the IL0. The large resistor on pin 5 helps reduce duty cycle variations with sweep. The linearity of input sweep voltage versus output frequency can be significantly improved by using an op amp as shown in Figure. 0.µF K 4.K N45 DUTY YLE 4.K 5K +V 4 5 6 AMPLITUDE 5 4 6 9 IL0 0K + - 4 0K K FREQ. IL0 4.K FIGURE 6. SINE WAVE OUTPUT BUFFEMPLIFIERS V- 0K 5M 0.004µF DISTORTION 0K -V FIGURE. VARIABLE AUDIO OSILLATOR, 0Hz TO 0kHzY
IL0 V + R FM BIAS DUTY YLE FREQUENY ADJUST 4 5 6 V + TRIANGLE OUT SQUARE WAVE OUT 9 IL0 SINE WAVE OUT INPUT VO IN PHASE DETETOR AMPLIFIER DEMODULATED FM R SINE WAVE ADJ. LOW PASS FILTER TIMING AP. SINE WAVE ADJ. V-/GND FIGURE 9. WAVEFORM GENERATOR USED AS STABLE VO IN A PHASE-LOKED LOOP HIGH FREQUENY SYMMETRY N5A (6.V) kω 500Ω 4.kΩ 4.kΩ MΩ kω 0kΩ 0kΩ,000pF +5V 4 5 6 9 LOW FREQUENY SYMMETRY - 4 + -V IN P4 kω OFFSET kω IL0 FUNTION GENERATOR 0kΩ + 50µF 5V +5V - 4 + SINE WAVE OUTPUT,900pF SINE WAVE DISTORTION -5V FIGURE. LINEAR VOLTAGE ONTROLLED OSILLATOR Use in Phase Locked Loops Its high frequency stability makes the IL0 an ideal building block for a phase locked loop as shown in Figure 9. In this application the remaining functional blocks, the phase detector and the amplifier, can be formed by a number of available Is (e.g., M444, NE56). In order to match these building blocks to each other, two steps must be taken. First, two different supply voltages are used and the square wave output is returned to the supply of the phase detector. This assures that the VO input voltage will not exceed the capabilities of the phase detector. If a smaller VO signal is required, a simple resistive voltage divider is connected between pin 9 of the waveform generator and the VO input of the phase detector. Second, the D output level of the amplifier must be made compatible to the D level required at the FM input of the waveform generator (pin, 0.). The simplest solution here is to provide a voltage divider to (R, R as shown) if the amplifier has a lower output level, or to ground if its level is higher. The divider can be made part of the low-pass filter. This application not only provides for a free-running frequency with very low temperature drift, but is also has the unique feature of producing a large reconstituted sinewave signal with a frequency identical to that at the input. For further information, see Harris Application Note AN0, Everything You Always Wanted to Know About the IL0.
IL0 Definition of Terms Supply Voltage (V SUPPLY ). The total supply voltage from to V-. Supply urrent. The supply current required from the power supply to operate the device, excluding load currents and the currents through and. Frequency Range. The frequency range at the square wave output through which circuit operation is guaranteed. Sweep FM Range. The ratio of maximum frequency to minimum frequency which can be obtained by applying a sweep voltage to pin. For correct operation, the sweep voltage should be within the range: ( / V SUPPLY + V) < V SWEEP < V SUPPLY FM Linearity. The percentage deviation from the best fit straight line on the control voltage versus output frequency curve. Output Amplitude. The peak-to-peak signal amplitude appearing at the outputs. Saturation Voltage. The output voltage at the collector of Q when this transistor is turned on. It is measured for a sink current of ma. Rise and Fall Times. The time required for the square wave output to change from % to 90%, or 90% to %, of its final value. Triangle Waveform Linearity. The percentage deviation from the best fit straight line on the rising and falling triangle waveform. Total Harmonic Distortion. The total harmonic distortion at the sine wave output. Typical Performance urves 0.0 SUPPLY URRENT (ma) 5-55 o 5 o 5 o NORMALIZED FREQUENY.0.0.00 0.99 0.9 5 5 5 0 5 0 SUPPLY VOLTAGE (V) 5 5 0 5 0 SUPPLY VOLTAGE (V) FIGURE. SUPPLY URRENT vs SUPPLY VOLTAGE FIGURE. FREQUENY vs SUPPLY VOLTAGE.0 00 NORMALIZED FREQUENY.0.0.00 0.99 0.9 0 0 0 0 TIME (ns) 50 0 50 5 o 5 o -55 o RISE TIME FALL TIME 5 o 5 o -55 o -50-5 0 5 5 5 TEMPERATURE ( o ) 0 0 4 6 LOAD RESISTANE (kω) FIGURE. FREQUENY vs TEMPERATURE FIGURE 4. SQUARE WAVE OUTPUT RISE/FALL TIME vs LOAD RESISTANE 9
IL0 Typical Performance urves (ontinued).0 SATURATION VOLTAGE.5.0 0.5 5 o 5 o -55 o NORMALIZED PEAK OUTPUT VOLTAGE 0.9 0. LOAD URRENT TO V - LOAD URRENT TO 5 o 5 o -55 o 0 0 4 6 LOAD URRENT (ma) 0 4 6 4 6 0 LOAD URRENT (ma) FIGURE 5. SQUARE WAVE SATURATION VOLTAGE vs LOAD URRENT FIGURE 6. TRIANGLE WAVE OUTPUT VOLTAGE vs LOAD URRENT..0 NORMALIZED OUTPUT VOLTAGE..0 0.9 0. 0. LINEARITY (%).0 0. 0.6 0 K K 0K M 0.0 0 K K 0K M FREQUENY (Hz) FREQUENY (Hz) FIGURE. TRIANGLE WAVE OUTPUT VOLTAGE vs FREQUENY FIGURE. TRIANGLE WAVE LINEARITY vs FREQUENY. NORMALIZED OUTPUT VOLTAGE.0 0.9 DISTORTION (%) 6 4 UNADJUSTED ADJUSTED 0 K K 0K M FREQUENY (Hz) 0 0 K K 0K M FREQUENY (Hz) FIGURE 9. SINE WAVE OUTPUT VOLTAGE vs FREQUENY FIGURE 0. SINE WAVE DISTORTION vs FREQUENY
Semiconductor Everything You Always Wanted to Know About the IL0 Application Note November 99 AN0. Author: Bill O Neil Introduction The 0 is a function generator capable of producing sine, square, triangular, sawtooth and pulse waveforms (some at the same time). Since its introduction, marketing and application engineers have been manning the phones explaining the care and feeding of the 0 to customers worldwide. This experience has enabled us to form articulate responses to the most frequently asked questions. So, with data sheet and breadboard in hand, read on and be enlightened. Question I want to sweep the frequency externally but can only get a range of 0: (or 50:, or :). Your data sheet says 00:. How much sweep range can I expect? Let s look at what determines the output frequency. Start by examining the circuit schematic at pin in the upper left hand corner. From pin to pin 5 we have the emitter-base of NPN Q and the emitter-base of PNP Q. Since these two diode drops cancel each other (approximately), the potential at pins, 5, and 4 are the same. This means that the voltage from to pin is the same as the voltage across external resistors and. This is a textbook example of a voltage across two resistors which produce two currents to charge and discharge a capacitor between two fixed voltages. This is also a linear system. If the voltage across the resistors is dropped from V to V, the frequency will drop by :. hanging from V to 0.V will also change the frequency by :. Therefore, by causing the voltage across the external resistors to change from say V to mv, the frequency can be made to vary at least 00:. There are, however, several factors which make this large sweep range less than ideal. Question You say I can vary the voltage on pin (FM sweep input) to get this large range, yet when I short pin to (pin 6), the ratio is only around 0:. This is often true. With pin shorted to, a check on the potentials across the external and will show 0mV or more. This is due to the V BE mismatch between Q and Q (also Q and Q ) because of the geometries and current levels involved. Therefore, to get smaller voltages across these resistors, pin must be raised above. Question How can I raise pin above without a separate power supply? First of all, the voltage difference need only be a few hundred millivolts so there is no danger of damaging the 0. One way to get this higher potential is to lower the supply voltage on the 0 and external resistors. The simplest way to do this is to include a diode in series with pin 6 and resistors and. See Figure. This technique should increase the sweep range to 00:. 0K FREQUENY LOG POT M FIGURE. VARIABLE AUDIO OSILLATOR, 0Hz TO 0kHz Question 4 0.µF 4.K N45 DUTY YLE O.K., now I can get a large frequency range, but I notice that the duty cycle and hence my distortion changes at the lowest frequencies. This is caused partly by a slight difference in the V BE sofq and Q. In trying to manufacture two identical transistors, it is not uncommon to get V BE differences of several millivolts or more. In the standard 0 connection with pins and connected together, there are several volts across and and this small mismatch is negligible. However, in a swept mode with the voltage at pin near and only tens of millivolts across and, the V BE mismatch causes a larger mismatch in charging currents, hence the duty cycle changes. For lowest distortion then, it is advisable to keep the minimum voltage across and around 0mV. This would of course, limit the frequency sweep range to around 0:. K 4.K 5 4 6 0.004µF 9 5K DISTORTION 0K +5V -5V opyright Harris orporation 99
Application Note 0 Question 5 I have a similar duty cycle problem when I use high values of and. What causes this? There is another error term which becomes important at very low charge and discharge currents. This error current is the emitter current of Q. The application note on the 0 gives a complete circuit description, but it is sufficient to know that the current charging the capacitor is the current in which flows down through diode Q 9 and into the external. The discharge current is the current in which flows down through diode Q. Adding to the Q current is the current of Q which is only a few microamperes. Normally, this Q current is negligible, but with a small current in, this current will cause a faster discharge than would be expected. This problem will also appear in sweep circuits when the voltage across the external resistors is small. Question 6 How can I get the lowest distortion over the largest frequency sweep range. First of all, use the largest supply voltage available (±5V or +0V is convenient). This will minimize V BE mismatch problems and allow a wide variation of voltage on pin. The potential on pin may be swept from V (and slightly higher) to / V +V) where V is the total voltage across the 0. Specifically for ±5V supplies (+0V), the voltage across the external resistors can be varied from 0V to nearly V before clipping of the triangle waveform occurs. Second, keep the maximum currents relatively large (ma or ma) to minimize the error due to Q. Higher currents could be used, but the small geometry transistors used in the 0 could give problems due to V E(SAT) and bulk resistance, etc. Third, and this is important, use two separate resistors for and rather than one resistor with pins 4 and 5 connected together. This is because transistors Q and Q form a differential amplifier whose gain is determined by the impedance between pins 4 and 5 as well as the quiescent current. There are a number of implications in the differential amplifier connection (pins 4 and 5 shorted). The most obvious is that the gain determines the way the currents split between Q and Q. Therefore, any small offset or differential voltage will cause a marked imbalance in the charge and discharge currents and hence the duty cycle. A more subtle result of this connection is the effective capacitance at pin. With pins 4 and 5 connected together, the Miller Effect as well as the compound transistor connection of Q and Q 5 can produce several hundred picofarads at pin, seriously limiting the highest frequency of oscillation. The effective capacitance would have to be considered important in determining what value of external would result in a particular frequency of oscillation. The single resistor connection is fine for very simple circuits, but where performance is critical, the two separate resistors for and are recommended. Finally, trimming the various pins for lowest distortion deserves some attention. With pins and connected together and the pot at pin and externally set at its maximum, adjust the ratio of and for 50% duty cycle. Then adjust a pot on pin or both pins and depending on minimum distortion desired. After these trims have been made, set the voltage on pin for the lowest frequency of interest. The principle error here is due to the excess current of Q causing a shift in the duty cycle. This can be partially compensated for by bleeding a small current away from pin 5. The simplest way to do this is to connect a high value of resistance (MΩ to 0MΩ) from pin 5 to V- to bring the duty cycle back to 50%. This should result in a reasonable compromise between low distortion and large sweep range. Question This waveform generator is a piece of junk. The triangle wave is non-linear and has large glitches when it changes slope. You re probably having trouble keeping the constant voltage across and really constant. The pulse output on pin 9 puts a moderate load on both supplies as it switches current on and off. hanges in the supply reflect as variations in charging current, hence non-linearity. Decoupling both power supply pins to ground right at the device pins is a good idea. Also, pins and are susceptible to picking up switching transients (this is especially true on printed circuit boards where pins and 9 run side by side). Therefore, a capacitor (0.µF or more) from to pin is often advisable. In the case when the pulse output is not required, leave pin 9 open to be sure of minimizing transients. Question What is the best supply voltage to use for lowest frequency drift with temperature? The 0AM, 0A, 0BM and 0B are all temperature drift tested at V = +0V (or ±V). A curve in the lower right hand corner of Page 4 of the data sheet indicates frequency versus temperature at other supply voltages. It is important to connect pins and together. Question 9 Why does connecting pin to pin give the best temperature performance? There is a small temperature drift of the comparator thresholds in the 0. To compensate for this, the voltage divider at pin uses thin film resistors plus diffused resistors. The different temperature coefficients of these resistors causes the voltage at pins and to vary 0.5mV/ o to maintain overall low frequency drift at V = 0V. At higher supply voltages, e.g., ±5V (+0V), the threshold drifts are smaller compared with the total supply voltage. In this case, an externally applied constant voltage at pin will give reasonably low frequency drift with temperature.
Application Note 0 Question Your data sheet is very confusing about the phase relationship of the various waveforms. Sorry about that! The thing to remember is that the triangle and sine wave must be in phase since one is derived from the other. A check on the way the circuit works shows that the pulse waveform on pin 9 will be high as the capacitor charges (positive slope on the triangle wave) and will be low during discharge (negative slope on the triangle wave). The latest data sheet corrects the photograph Figure on Page 5 of the data sheet. The 0% duty cycle square wave was inverted, i.e., should be 0% duty cycle. Also, on that page under Waveform Timing the related sentences should read controls the rising portion of the triangle and sine-wave and the state of the square wave. Also, the falling portion of the triangle and sine wave and the 0 state of the square wave is: Question Under Parameter Test onditions on Page of your 0 data sheet, the suggested value for Min and Max duty cycle adjust don t seem to work. The positive charging current is determined by alone since the current from is switched off. (See 0 Application Note AN0 for complete circuit description.) The negative discharge current is the difference between the current and twice the current. Therefore, changing will affect only the discharge time, while changing will affect both charge and discharge times. For short negative going pulses (greater than 50% duty cycle) we can lower the value of (e.g., = 50kΩ and =.6kΩ). For short positive going pulses (duty cycles less than 50%) the limiting values are reached when the current in is twice that in (e.g., = 50kΩ). This has been corrected on the latest data sheet. Question I need to switch the waveforms off and on. What s a good way to strobe the 0? With a dual supply voltage (e.g., ±5V) the external capacitor (pin ) can be shorted to ground so that the sine wave and triangle wave always begin at a zero crossing point. Random switching has a 50/50 chance of starting on a positive or negative slope. A simple AND gate using pin 9 will allow the strobe to act only on one slope or the other, see Figure. Using only a single supply, the capacitor (pin ) can be switched either to or ground to force the comparator to set in either the charge or discharge mode. The disadvantage of this technique is that the beginning cycle of the next burst will be 0% longer than the normal cycle. Question How can I buffer the sine wave output without loading it down? The simplest circuit is a simple op amp follower as shown in Figure A. Another circuit shown in Figure B allows amplitude and offset controls without disturbing the 0. Either circuit can be D or A coupled. For A coupling the op amp non-inverting input must be returned to ground with a 0kΩ resistor. Question 4 Your 0 data sheet implies that all waveforms can operate up to MHz. Is this true? Unfortunately, only the square wave output is useful at that frequency. As can be seen from the curves on page 4 of the data sheet, distortion on the sine wave and linearity of the triangle wave fall off rapidly above 00kHz. Question 5 Is it normal for this device to run hot to the touch? Yes. The 0 is essentially resistive. The power dissipation is then E /R and at ±5V, the device does run hot. Extensive life testing under this operating condition and maximum ambient temperature has verified the reliability of this product. Question 6 How stable are the output amplitudes versus temperature? The amplitude of the triangle waveform decreases slightly with temperature. The typical amplitude coefficient is -0.0%/ o, giving a drop of about % at 5 o. The sine output is less sensitive and decreases only about 0.6% at 5 o. For the square wave output the V E(SAT) goes from 0.V at 5 o to 0.V at 5 o. Leakage current in the state is less than a few nanoamperes even at 5 o and is usually negligible. 5K 4 5 6 0 9-5V N49 0K OFF N94 N94 ON +5V STROBE +5V (>0V) -5V (< -V) FIGURE. STROBE-TONE BURST GENERATOR
Application Note 0 4 5 6 0 + - 4 5 6 0 AMPLITUDE 0K + - 0K 4.K V- V- FIGURE A. FIGURE B. FIGURE. SINEWAVE OUTPUT BUFFEMPLIFIERS Schematic Diagram 4