CEM3320

CEM3320 CES | Alldatasheet

Document overview

• Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
• PDF pages: 6

Technical content

The CEM 3320 is a high per- demanding applications, pro- formance voltage controlled vision has been made to allow four-pole filter complete with trimming for improved control ‘on-chip voltage controllable voltage rejection. Each filter resonance. The four independent section features a novel variable a at sections may be interconnected gain cell which, unlike the 3 4 eat to provide a wide variety of filter traditional cell, is fully tempera- <0 ad responses, such as low pass, high —_ ture compensated, exhibits a . rN q a pass, band pass and all pass. A better signal-to-noise ratio and ) $ hee gk single input exponentially con- generates its low distortion pre- ba ad bis | trols the frequency over greater dominantly in the second . Pie than a ten octave range with harmonic. The device further 1 ¥ 2 co little control voltage feed- includes a minus two volt regu- a through. Another input controls _lator to ensure low power dis- the resonance in a modified sipation and consequent low 1 linear manner from zero to low warm-up drift even with £15 distortion oscillation. For those _volt supplies. Circuit Block and Connection Diagram i FREQ. CNTL. Features y ner B Low Cost R -15V ® Voltage Controllable Re Re F REE a5 SIGNAL Frequency: 12 octave range 100K 291K 100K 15K 2 10K 1.8K = OUTPUT minimum [4 300pF | 1uF @ Voltage Controllable +18V Resonance: From zero to Cp | 300pF op * oscillation Ze) C18) 2 NO WO H Accurate Exponential Re | AB [INCEN | m7 Frequency Scale gS 8 By > Pray VY | res. @ Accurate Linear Resonance x bed REG. BIAS Scale > > B Low Control Voltage Feed- ToP through: -45qB typical view P) rs — @ Filter Configurable into Low Pass, High Pass, All Pass, etc. ® Large Output: 12V.P.P. Re six Mt Low Noise: -86aB typical 20K tte Low Distortion in Passband: 0.1% typical = cp ltr Rac @ Low Warm Up Drift R Ae po wr 100K B Configurable into Low aK 1K Oo L Distortion Voltage Controlled - - RESONANCE Sine Wave Oscillator

Electrical Characteristics Application Hints : Voc = +15V Rr = 100K Ta = 25°C ; Supplies Parameter Min. Typ. Max, [unis | dissipation, the negative supply is Pole Frequency Control Range 3500:1 10,000:1 [|__| regulated at -1.9 volts with an Sensitivity of Pole Frequency internal shunt regulator. This Control Scale, Midrange 87.5 60 625 | mvidecade | not only reduces warm-up drift Tempco of Pole Frequency of the pole frequencies at power Control Scale 3000 3300 3600 ppm turn-on, but also allows vir- Exponential Error of Pole tually any negative supply Frequency Control Scale! - 4 12 % greater than -4 volts to be used. i Gain of Variable Gain Cell The current limiting resistor, at Vor0. 07 09 1.3 Ree, must always be included : Max Gain of Variable Gain Cell 24 3.0 3.6 and is calculated as follows: Tempco of Variable Gain Cell2 ~ 500 1500 ppm Output Impedance of Gain Cell2 os 1.0 2.0 Mo. Ree = Vee -27V Pole Frequency Control 0.008 Feedthrough - 60 200 mv As can be seen from the Block Pole Fi Warm-up Drift - 5 ‘ % ‘ . eT 1s % Diagram, an internal 1002. re- im of Resonance sistor is in series between the Control Element at RUA 8 1.0 1.2 mmhos regulator and pin 13. This resis- mn anes inable ° as re Before Oscillation 20 30 - 0B for which allows for vning Resonance Control Feedthrough3 = 0.2 16 v of the control voltage feed- i . through (explained in further Output Swing At Clipping 10 12 14 VPP. detail below) results in an actual Output Noise re Max Output4 -76 -86 - 4B voltage at pin 13 of around ~2,7 Rejection in Bandreject 73 83 - aB volts, Distortion in Passband5.7 = 01 0.3 % Although the circuit was Distortion in Bandreject6.7 = 03 1 % designed for a positive supply Distortion gf Sine Wave of +15 volts, any voltage between Oscillation’ - 0.5 1.5 % +9 and +18 volts may be applied Internal Reference Current, IREF 45 63 85 HA to pin 14. The only effect, other Input Bias Current of Frequency than power dissipation, is the Control Input 0.2 0s 15 BA maximum possible peak-to-peak Input Impedance to Resonance output swing in accordance Signal Input 27 3.6 45 Ko with: Buffer Slew Rate 15 3.0 Vius Vout (V.P.P.) = Vee - 3V Buffer Input Bias Current (lee=8ma) #8 430 £100 nA . . Buffer Sink Capability 4 5 63 mA Operation of Each Filter Buffer Output Impedance2 75 . 100 200 Q Stage Positive Supply Range 49 ~ +18 v Each filter stage consists of a Negative Supply Range? 4 ~ ~18 v variable gain cell followed by a Positive Supply Current 3.8 5 6.5 mA high input impedance buffer. Note 1: -25mV < Vg < #155mV. Most of this error occurs in upper two octaves, The variable gain cell is a current- Note2: Vo =0 in, current-out device (as opposed Note 3: Untrimmed. 0 < Igp < 100HA to the traditional eo age Note 4: Filter is connected as low pass and set for 20 KHz cut-off frequency. current-ou 1 ‘evice) whose by Note 5: Output signal is 348 below clipping point. the fallow our. is given by : Note 6: Output signal is 3dB below passband level, which is 3B below clipping point. In general, the following expression: this is worst case condition. Vel. Note 7: Distortion is predominantly second harmonic. lout = (IREF - lin) Aig e YC/¥T Note 8: Sinewave is not clipped by first stage. Note 9: Current limiting resistor always required. where Vr = KT/q, Vc is the i 2 i

voltage applied to pin 12, Aig i eye rire oan ay ere Voltage Between Veg and Veg Pins +22V,-0.5V and Voltage Between Vcc and Ground Pins +18V,-0.5V | ABVcc - .65V Voltage Between Veg and Ground Pins -4V,+0.5V 'REr = “To0K" Voltage Between Cell Input and Ground Pins +0.5V,-6V : Voltage Between Frequency Control and "426% Ground Pins £6V, As the input to the variable Voltage Between Resonance Control and cell is a forward biased diode to Ground Pins 42V,-18V ground, it presents sesontially Current Through Any Pin £40mA See oSOnY ahaa Storage Temperature Range -55°C to +150°C ground. The required input Operating Temperature Range -25°C to +75°C currents may therefore be obtained with resistors ter- | minating at this input node. i For normal operation of any The output impedance of the __ If the signal is from the output filter type, each stage is set up variable gain cell, although high, _ of a previous filter section, it : with a feedback resistor, Re, has a finite value. This imped- will have a quiescent level of from the buffer output to the ance is reflected back to the A6Voc (6.9 volts for a +15 volt variable gain cell input, and with input as an A.C. resistance of supply). Therefore, part of lin the pole capacitor, Cp, connected nominally 1 megohm in parallel __will be supplied by this voltage to the output of the variable with the feedback resistor, Rr, through Re while the remainder gain cell. This setup is shown regardless of control voltage will be sourced through Rr. in Figure 1. In the D.C. value. The pole frequency of The voltage gain in the pass- quiescent state, the buffer out- each filter section is determined _ band is given by Reg/Rc. In put will always adjust itself so by the total equivalent feedback general, this gain should be set that a current equal to IRer resistance, Req, and the pole to unity for stages two, three i flows into the input. capacitor in the expression: and four. The input resistor to For lowest control voltage stage one can be scaled for any feedthrough and maximum fp = Alo evelVT size of the external input signal. peak-to-peak output signal, the PO 2 Race The resistance value should be quiescent output voltage of each selected so that the maximum buffer, Vopc, should be: where: external input signal produces = . * the maximum passband output Vooe = -46Vec Rea = ig + IMQ* signal before clipping. | Thus, in the simple case of Re +1MQ* Figure 1, Re is calculated as follows: 1-60%, +100% - AE Re= Vone = .65V Signal Coupling into a 'REF Filter Section . = 100K nominal For the filter section to provide the low pass function, the input © oO Since Imef can vary +25%, signal is coupled via a scaling wer worl ourPuT (Lo 2) Vopc can vary nearly 30% from —_ resistor, Rc, into the input. If t d device to device using a standard __the signal is the external input to - cap + uy =taee | 5% resistor for Re. In the typical the entire filter, it will in general Toowencets in oUIeSeENT case where Vcc = +15V, IReF is have a D.C. quiescent voltage STATE i 63uA nominal, and the D.C. level of zero, and all of Ii equal j oout of each buffer should be ‘to Ipef for the first stage will be FIGURE 1: ONE OF FOUR STAGES i set for +6.9V nominal. provided by its feedback resistor. 3 ;

To generate the hi-pass func- _resonance feature. Note that due tion, the input signal is coupled —_to the configuration of the FREQ, into the variable gain element resonance feedback, the reso- Ty CNTL. i output via the pole capacitor, nance frequency of the high-pass cv. otsk |e] INPUT level is blocked by the capacitor higher than that of the low-pass, 100K TRIM >a] and Ij equal to Iperf foreach —_ while the resonance frequency waa input is supplied only through of the band-pass and all-pass +H5VS— 1.8K, the feedback resistors. The will be 1/2.4 = .42 times lower OT] | voltage gain in the pass band is than that of the low-pass, for the OOO O64 OF Oo + simply unity, regardless of the same component values. For the Cp [18 17 16 15 14 13 12 11 10h = value of Re. For best results, the state variable, resistor Raq adds J00pF ) CEM 3320 xO SteNaL output impedance of whatever _positive feedback to increase Th 2 34 5 6 7 8 9{=2 ourtuT i is generating the external input the maximum Q, which is other- oe ol ol ceo ome} Ty = signal to stage one should be low _ wise limited by the reflected R = i compared to Re/4. 1MQ, impedance across the RF ORE cp ?)S} | Arc integrators. 3 S100KS sooo |S 100K. ' Sample Filter Circuits The Block Diagram shows the Fole Frequency Control [TT resonance external components connec- Scale SIGNAL INeUT CNTL. INPUT tions for a four-pole, low-pass The current gains of each of the filter designed to operate off four sections (and consequently FIGURE 2: HI PASS FILTER WITH V.C. RESONANCE +15 volt supplies, The values their pole frequencies) are for Rr, Rc, and Rg were chosen controlled simultaneously with so that a) when the 1 megohm a voltage applied to pin 12. (pin 8), a separate contro! cur- reflected resistance is in parallel Since the scale is exponential rent input with a modified linear with Rr, the gain of stages two, with the standard 18mV/octave scale (pin 9}, and a current three and four is unity, and b) {60mV/decade}, an input atten- —_ output internally connected to with the buffer outputs at the uator network will in most cases the input of stage one. With an proper quiescent level of 6.9 be required. An increasing posi- _ impedance of 3.6K +900, the volts, the total current into each __ tive control voltage lowers the input is referenced to ground; input is the required 63uA:.For pole frequencies of the filter. thus, connection to the filter stage 1, all of this quiescent For best results over a thousand- output will require a coupling current is sourced by the feed- —_—to-one control range, the voltage capacitor. back resistor. For stages two, on pin 12 should be maintained three, and four, 63uA is sourced between -25mV and +155mV. by the feedback resistor, while Unlike the typical variable FREQ. 70pA is sourced by the coupling transconductance cell used in a8 = CNTL. resistor for a total sourced cur- —_ most V.C. filters, the four stages sou S Be cw. 1 waror Y rent of 133A. Thus, to end up in the CEM 3320 are fully tem- ak = [tang 100K with a net quiescent input perature compensated. The only = | vex tee current of 63uA, 70uA is sunk remaining first order temperature Re | ore * 18K; out of the input by bias resistor, effect is that of control scale x 1d db bad Sd + Rg. sensitivity (1/V7). This effect SSS kh 17 16 15 14 13 12 11 10} = : If connecting the filter input —_ may be compensated in the eye) cem 3320 ue to an external signal causes the = usual manner with a +3300ppm “T2345 678 8|pey siaNaL D.C. level of the filter output to tempco resistor (Tel Labs 81). yey yyy change more than several volts, ” = |2 it is recommended that an input F cp S| |e, coupling capacitor be used such Resonance Control! ‘00K sooaey” ||| toon / as shown in Figure 4. The variable gain cell used to [| RESONANCE Figures 2, 3,4, and 5show —_control the amount of resonance _ ONTL. INPUT high-pass, band-pass, all-pass, is the traditional transconduc- SIGNAL INPUT. i and state variable realizations, all tance type of amplifier. It has a FIGURE 3: BAND PASS FILTER WITH V.C. RESONANCE with the voltage controlled separate signal voltage input . 4 j

Control of the transconduc- While operating the filter in tance is accomplished with a the resonant mode, care should FRea. : current input. As the control in- _be taken not to overload the eNTt. | put is alow impedance summing input to the filter. If the signal [ | “vp |] neu | node at a potential near ground, —_ output of stage one is allowed to Rr. x} ov. SU5K |S the control current may be become clipped, then not only x 3], [REL Tag] == | 100K i derived from the resonance con- _ will the apparent resonance 2 eye Gy trol voltage with an input re- of the signal at the filter output Ag 8) +5VS= 18K i sistor, Rac, terminated at pin9. appear to be reduced, but the we SRE. tp! ca ae ° This resistor should be selected _D.C. level of the output signal RS ES eid te tte] +] : so that the maximum available will shift, ) cem 3320 - resonance control voltage pro- When the resonance control hue duces the maximum desired is advanced until sustained asl 9 sama control current, oscillations are produced, ad- 220K’ L | er Figure 6 shows a graph of vancing the resonance control op Te the transconductance versus further will merely increase the Re ole] | Rac control current. As can be seen, amplitude of the oscillation. A FA Tt s 1O0KT nes. the slope of the curve becomes lesser effect is the shift of the Coo INPUT gradual as the control oscillation frequency. For : current increases. This feature minimum shift (typically less + tHe Ser i allows the resonance to be con- than 0.5%), the oscillation H trolled with finer resolution as amplitude should be kept below FIGURE 4: ALL PASS FILTER WITH V.C. RESONANCE the critical point of oscillation the clipping level of the first is approached, stage output. Allowing the with a series resistor and trim j The maximum control oscillation to be clipped will pot. The fixed resistor, Re, and current is therefore selected in produce frequency shifts in series trim pot, Rr, should be | accordance with the amount of excess of 5%. selected so that the current control sensitivity which is into pin 13 may be adjusted desired at the top of the control Other Uses of the from 5mA to 12mA, Or: range. The value of the input Resonance Control Cell Vee -3.2V resistor, Rry, is then selected . R- =e depending on where in the con- Other than controlling the Bam \\ trol scale oscillation is desired resonance, the variable trans- i to begin (when the control conductance amplifier may be voltage is 90% of the maximum used as an independent VCA norcraureur past aurear value, for instance). The follow- controlling the amplitude of the ing formula may be used: input signal to the filter. Or the to av rea. cell may be set up as a sym- Pass enTL. } metrical limiter/clipper for ouTPUT iy uk (npuT Re =3.6K* (Gmosc Rea -1 ) either preventing large dynamic Re rans Fr | yi RIS se A input signals from overloading 100K 3 ‘ose the filter or for providing addi- +15V Re 1K *425% tional coloration to the input R To! signal. ex Ag] pPPHALBLGOO ¢ . 1817 16 15 14-13-1211 10 where Gmogc is the transcon- 110K b cem 3320 ductance corresponding to the Pole Frequency Control t2aase7es|= control current at which oscilla- Voltage Rejection -18v SRaSRclo oro tion is desired to begin; and ge Rej reagan TLIS TTT where Aogc is the overall gain The D.C. voltage shift at the T Sas THK | from the resonance signal input__ filter output due to the fre- Ste SmeS aqgionn PEL St. 1 resistor, Rr}, to the filter output quency control voltage may be 110K = uF] 33M INPUT i required to sustain oscillation. minimized by adjusting the Spur [| i If the gain of stages 2, 3 and 4 current into the minus supply HI PASS are unity, then Aggc = 12dB or _pin, pin 13. This is accomplished outpur -8V 4 in the case of the low pass by replacing the negative supply FIGURE S: STATE VARIABLE FILTER WITH V.C. “0” filter. current limiting resistor, Ree, 5 ;