AS3394

AS3394 ALFA | Alldatasheet

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Technical content

AS “АLFA RPAR” Joint Stock Company ALFA Riga, Latvia www.alfarzpp.lv; alfa@alfarzpp.lv 2019 v.1 AS3394E AS3394E AS3394E µP CONTROLLABLE SYNTHESIZER VOICE

FEATURES

• Complete synthesizer Voice on a Chip
• Sample & Hold buffers on-chip for easy interface to a µP
• Fully temperature compensated VCO
• Independently selectable VCO waveforms
• Sub-oscillator output
• Separate saw-tooth output
• Separate VCO and filter sections allowing design flexibility
• Constant Loudness vs Resonance VCF
• Rich Sounding VCF Design
• Filter FM routing for more Timbres
• Low Noise, Low Feedthrough VCA SOIC-24 300mil, 1.27 mm

DESCRIPTION

The AS3394E is a complete analog music synthesizer voice -on-a-chip intended for software control by a microprocessor system. Included inside the compact 24 pin package is fully temperat ure compensated, wide range, voltage controlled oscillator providing sub -oscillator, triangle, saw -tooth, and pulse waveforms; a voltage controlled mixer for adjusting the balance between the internally generated VCO waveforms and any external signal; a dedicated four -pole low -pass voltage controlled filter with voltage controlled resonance; a modulation amount VCA for modulating the filter frequency by the triangle waveform output of the VCO; and a final VCA for allowing the outpu t to be enveloped. Envelope control for both the VCF and final VCA may be provided by either a hardware envelope generator such as the AS3310 or through software. All eight control inputs are provided with internal very high input impedance, low bias curre nt buffers. Thus interface to a microprocessor system may be accomplished simply with a single DAC, 4051 -type CMOS multiplexer, and 8 hold capacitors. Requiring a bare minimum of other external components, the AS3394E is ideal for low cost polyphonic or polytimbric musical instruments featuring rich, analog sound. FUNCTIONAL BLOCK DIAGRAM 11 121098 X 11K D-Trig TC GEN ex BB B BB BB B B TRNGL. TRNGL. ICO to saw conv.

4 LEVEL

e x ΔGm ΔGm ΔGm ΔGm - + + + + VCA41K 1K VCA1 1KAS3394E 24 22 21 2023 19 18 17 16 15 14 13 1 2 3 4 5 6

AS “АLFA RPAR” Joint Stock Company ALFA Riga, Latvia www.alfarzpp.lv; alfa@alfarzpp.lv 2019 v.1 AS3394E AS3394E

Electrical Characteristics

PARAMETER MIN TYPICAL MAX UNITS VCO Specifications Frequency Range 12Hz - 20KHz CV Input Range -4.0 - +4.0 Volts CV Scale Factor -0,65 -0,75 -0,85 V/Octave Exponential Error (<8KHz) - 0,3 1,0 % Temperature Coefficient -500 0 500 ppm Reference Voltage (pin 1-3) 1,1 1,2 1,3 V CV Input Current - 0,3 3 nA Frequency at CVin = 0.0V 330 500 750 Hz Sub-oscillator output (D-Trigger RL=10kΩ): Maximum voltage output 1,8 2,0 2,2 V Minimum voltage output -2,2 -2,0 -1,8 V Saw-tooth output : Maximum current output 40 50 60 µA Minimum current output -40 -50 -60 µA WAVE OUTPUT Maximum current output 70 80 90 µA Minimum current output -70 -80 -90 µA WAVE SHAPER Waveform Select Thresholds : - Pulse -0,6 -1,0 -1,8 V - Triangle -0,2 -0,35 -0,5 V - Triangle + Sawtooth 0,9 1,2 1,5 V - Sawtooth 2,3 3,0 3,9 V Wave Select Input Current - -50 -300 nA PWM PWM Input Current - 0,5 5,0 nA Pulsewidth CV for 0% Pulse 0 - 0,2 V Pulsewidth for 100% Pulse 1,9 - 2,2 V Pin Information Pin No Pin Name Description Pin № Pin Name Description

1 Iref Reference Current 13 Mix_Bal Mixer Balance CV

2 VCO_CF VCO Input CF 14 VCA2 VCA2 Input 2

3 -Vee Negative Supply Voltage 15 Filt_Res Filter Resonance CV

4 Ct Timing capacitor 16 C1 Filter capacitor 1

5 D-Trig Out D-Trigger Output 17 C2 Filter capacitor 2

6 Mod_Amt Filter VCA3 modulation control 18 C3 Filter capacitor 3

7 Wave_Sel Wave Select CV Input 19 C4 Filter capacitor 4

8 PWM_CV PWM CV 20 VCF _CV Filter control voltage

9 Sawtooth Out Sawtooth Output 21 Cs Servo-capacitor

10 Wave_Out Wave Output 22 VCA5_CV VCA5 gain CV

11 VCA1 VCA1 Input 1 23 VCA5_Out VCA5 Output

12 GND Ground 24 +Vcc Positive Supply Voltage

AS “АLFA RPAR” Joint Stock Company ALFA Riga, Latvia www.alfarzpp.lv; alfa@alfarzpp.lv 2019 v.1 AS3394E AS3394E Continuation of Table FILTER MODULATOR Max Modulation Depth 0,01X - 2X Freq. CV for 0% Modulation -0,3 - 0,1 V CV for Max Modulation 3 - 4 V CV Input Current - -0,5 -5 nA FILTER INPUT MIXER External Input Level (VCA1, VCA2) - ±40 - mV @ 5% THD External Input to Output Gain 3,6 4,5 5,6 mmho CV Input Current - -0,3 -3 nA External Input Bias Current - -0,3 -0,7 µA CV Feedthrough -30 0 30 µA 4-POLE LOW-PASS FILTER CV Input Range -3 +4 V CV Scale Factor -0.33 -0.38 -0.43 V/Octave Frequency @ CV = 0.0V 900 1300 1800 Hz Frequency CV Input Current - -0,3 -3 nA Resonance CV : No Resonance 0 - 0,3 V Resonance CV: Oscillation 2 2,5 3 V FINAL VCA Attenuation at CV = 0 80 90 - dB CV for Maximum Output 3,8 4 4,3 V CV Scale Factor (20-100dB) 4) - 20 - dB/V Triangle Wave Output Level 190 250 325 µA pp Triangle + Sawtooth Output 255 330 430 µA pp Sawtooth Output Level 150 200 260 µA pp Square Wave Output Level 120 160 210 µA pp All Waves On Output Level 300 400 520 µA pp CV Feedthrough - ±0,3 ±3 µA CV Input Current - 0,3 3 nA POWER SUPPLIES Positive Supply Range +4,75 - +8 V Negative Supply Range -4,75 - -16 V Positive Supply Current 13 16 21 mA Negative Supply Current -13 -16 -21 mA 1. Most of error occurs at frequency extremes. Typical value is at mid-range 2. When switching from the no waveforms condition. 3. Filter frequency C.V. = 0V. 4. This scale holds from max attenuation to approximately 20 dB of attenuation. Thereafter, scale is approximately linear.

AS “АLFA RPAR” Joint Stock Company ALFA Riga, Latvia www.alfarzpp.lv; alfa@alfarzpp.lv 2019 v.1 AS3394E AS3394E APPLICATION HINTS POWER SUPPLY The AS3394E was designed to operate from +5V and -6.5V supplies. The non -standard negative supply was necessary not to compromise the VCO frequency resolution, which ranges from -4 to +4 volts, in favor of a -5V supply (this is because there needs to be 4 diode dr ops for the current mirrors ). Any one of the readily available 3-terminal regulators may be used to supply the -6.5V negative supply. Since the stability and jitter of the VCO are directly affected by noise on the positive supply, a supply as stable and clean as possible should be use (not the +5Vdigital supply) Maximum supply allowable across the device is 25 volts. VCO The control scale of the VCO is temperature compensated with an internal +3300ppm tempco generator and multiplier. Thus, as chip temperature changes, the control voltage applied to the exponential generator changes proportional to temperature, effectively canceling the -3300ppm tempco of the control scale. The resistor Rt from Pin 1 to the negative supply sets up an internal reference current for the exponential voltage-to-current converter. Its value and that of timing capacito r Ct determine the nominal initial frequency of the VCO at zero CV applied. The equation is: Fout = (Vref)/(Vcc x Rt x Ct) where Vref is the voltage across pins 1 and 3, nominally 1 ,2 volts. The other consideration is the current range of the V to I conv erter, which is optimized for a range of 300nA to 80 µA. Using 80 µA as an upper limit, the timing capacitor is chosen by: Ct = (80µA)/(Fmax1 x Vcc) where Fmax1 is the maximum frequency at the best accuracy (80µA). In a typical application, suppose the be st accuracy is in the range of 32Hz to 8KHz. Thus Fmax1 is 8KHz, and Ct is calculated to be 2nF. The middle of this range is 500Hz which is set to Fout. Therefore Rt calculates to 240K. Note that since the VCO input range is -4 to +4 volts with a scale fac tor of 0,75 V/Octave, the VCO will sweep from 12Hz to 20KHz. A -5V negative supply can be used if the sweep range is reduced. In this case, Ct = 4nF and Rt = 65K. Since the VCO was designed to be software adjusted, a simple multiplier was used with sligh t non-linearity at its two extremes. Therefore, for best results, it is recommended that the scale factor and scale linearity be auto-corrected through software means. Output Saw-tooth Out (pin 9) - saw-tooth signal with an internal VCO frequency span o f ± 50 μA. This output can be loaded on a 1 kΩ resistor and the saw -tooth signal can be fed directly to the Ext In1 or Ext In2 inputs, as well as used for other purposes. The maximum signal voltage at this output should not exceed ± 200 mV. Output of a Sub-Oscillator (pin 5) - rectangular pulses with the frequency of the internal oscillator VCO divided by 2 (square wave one octave below the fundamental frequency). The output voltage swing is ± 2 V; this output can be loaded onto a resistor with a resistance of at least 10 kΩ. This signal can also be mixed with other used signals.

AS “АLFA RPAR” Joint Stock Company ALFA Riga, Latvia www.alfarzpp.lv; alfa@alfarzpp.lv 2019 v.1 AS3394E AS3394E WAVEFORM SELECTION By applying the control voltage in the range from -2 V to +4 V to the Wave Select CV input (pin 7), you can select the following waveforms at the Wave Out output: Pulsed (PWM), Triangular, Triangular + Saw-tooth and Saw-tooth. The specific value of the control voltage for selecting the waveform is given in the table of parameters. The pulse width may be turned off simply by setting the Pulse Width control vol tage slightly negative to ensure a pulse width of 0%. A unique circuit on -chip keeps the average DC level of the pulse waveform constant regardless of duty cycle, so that pulse width may be modulated without annoying control signal feedthrough. The relati ve amplitudes of the three waveforms have been set as foll ows to give approximately equal loudness: The triangle is 27% larger than the saw-tooth, which is about 27% larger than the pulse wave. EXTERNAL INPUT External inputs VCA1 and VCA2 can receive any signals up to ± 40 mV. Normally, a resister divider is required to attenuated the input signal to this level. The resistance to ground should be 1k to keep the VCA balanced, and the i nput signal should be capacitive ly coupled to minimize control voltage f eedthrough. A small adjustable offset of ±20mV may be applied to this input to further reduce CV feedthrough. The control voltage range at the Mixer Balance CV pin 13 input is from -2 V to +2 V. The VCA1 and VCA2 amplifiers are controlled in antiphase, at -2 V VCA2 is fully switched on, at +2 V VCA1 is fully switched on. Signals from VCA1 and VCA2 inputs are nominally in equal balance - each being 6dB down from its maximum, when the control voltage is at zero volts. The control scale is roughly audio taper: the first 20dB of range is linear while the remaining 60dB is exponential. This external input is ideal for adding noise, a signal from a second VCO, or both. VCF Able to sweep over a minimum of 14 octaves, the filter is the classical wide range 4 -pole low-pass type designed for musical instruments. The control scale has twice the sensitivity as that for the VCO: it is 3/8V per octave. The first 3 stages of the filter are unity gain transconductors while the last stage provides a gain of 57 (and consequently has a transconductance of 1/57 of the first three). This requires three equal capacitor values, and the fourth is 1/57th of the other value. The frequency of the -12dB point on the cut-off slope is given by: Pzcv = Gm/(2 x pi x Ceq) = (Iref)/(4 x pi x Ceq x VT) where V T = KT/q = 26mV at 20 oC. The reference current is set up internally an given a +3300 ppm to compensate for the VT -3300ppm tempco. Thus this equation can be reduced to: Pzcv = 4,3 x 10E-5/Ceq Note that due to internal resistor tolerances, the 4,3E-5 term can vary 40% part-to-part. Selection of the 4 filter capacitors is again determined by the maximum desired cut -off frequency and optimum operating range of the OTAs. The range has been optimized for an operating range of 5 umho to 5 mmho. Thus we can calculate C as follows: C = 5E-3/(2 x pi x Fmax)

AS “АLFA RPAR” Joint Stock Company ALFA Riga, Latvia www.alfarzpp.lv; alfa@alfarzpp.lv 2019 v.1 AS3394E AS3394E As an example, assume the highest cut -off frequency is 24KHz . C1 -C3 becomes 33nF and C4 is 33nF/57 = 580pF. The frequency at zero control volts is approximately 1300Hz; 24KHz will be reached in 4,2 octaves, or at -1,6V. The filter can be opened up to >40KHz using these values, but CV feedthrough becomes excessive. The resonance VCA feedback circuit has been designed so that as the resonance is increased the apparent loudness remains constant, providing a much riche r resonant sound. Note, however, that the peak -to-peak level of a pule/square wave actually doubles as resonance is increased, due to the ringing on its fast edge transitions. VCF MODULATION The modulation VCA allows the VCO triangle wave to modulate the reference current of the VCF, and hence the cut-off frequency. The Modulation Amount control voltage (Pin 6) controls the 'depth': at maximum setting the VCF is swept from a very low value to twice the unmodulated frequency. Since the modulation is linear , the apparent filter frequency does not shift as modulation is increased. One application of this control is to set the filter into oscillation for obtaining linear audio FM of one VCO by another (using the VCF as a VCO). However, an equally interesting application is to audio FM the filter while it is filtering normally. The result is strong timbral effects, especially with some resonance added. FINAL VCA The final VCA is a low noise, low control feedthrough design which substantially reduces fast enve lope click and pop noises without the need for a trimmer. The output of the filter is essentially AC coupled to the VCA input by means of the bypass capacitor connected to Pin 21. Thus, its value along with the internal 11K resistor sets the low corner fre quency; a value of 4,7µF results in a -3dB point of 3Hz. This pin may also be used to extract the filter output signal before it is passed through the VCA. The final VCA control scale is approximately audio taper. The first 20dB of attenuation from a contr ol voltage of +4V to +2 ,5V is linear. The next 60 to 80dB of attenuation is from +2 ,5V to 0V is exponential. This allows the natural sound of exponential decays to be produced with simple linear envelope control, which is much simpler to generate in software. The signal output at Pin 23 is a current with a voltage compliance of Vee+1 to V cc-1. This allows the outputs of multiple 3394s to be mixed together by connecting all Pin 23s together. The summed current can then be converted to a voltage simply by a resistor to ground, or an op -amp with feedback resistor. The major portion of the 40% tolerance on the maximum output swing (nominally ±210µA) is due to the monolithic diffused resistors setting the currents. Although the output variations part -to-part are typically much less than this (about 5 -10%, ed.) , output levels as well as the filte r initial frequency may be more closely matched by matching the resistance between the Vcc and Vee pins. INPUT CONTROL VOLTAGE BUFFERS With the exception of Waveform Select whose control voltage is not critical, the input bias current to all control inputs is typically less than 1 nA, and have maximum values of 3 and 5 nA. Hold capacitor values can be in the range of 2 to 20 nF before causing multiplexing problems and DAC output instability. The amount of droop is given by: Vdroop = (Ibias – Tupdate) / Chold With a hold capacitor of 10nF and update time of 10 ms, maximum droop would be 5 mV or between 0 ,06 and 0,12% of full scale. Typically, the droop is a factor of 10 less than these worst case values.

2019 v.1 AS3394E µP controllable voice block and external connections

2019 v.1 24-Lead Standard Small Outline Package (SOIC_W) Wide Body Dimensions shown in millimeters and (inches)

Revision history

11-Mar-2019 1 Short version 1