Kuliah Minggu 3 Elektronika dasar Jurusan Teknik Elektro 2007

SUMMING AMPLIFIER Recall inverting amplifier and If = I1 + I2 + … + In VOUT = -Rf (V1/R1 + V2/R2 + … + Vn/Rn) Summing amplifier is a good example of analog circuits serving as analog computing amplifiers (analog computers)! Note: analog circuits can add, subtract, multiply/divide (using logarithmic components, differentiat and integrate – in real time and continuously.

PENGKONDISI SINYAL (aplikasi penjumlah) R2 Vref – + Vo R diinginkan Keluaran V0 00 C  0 Volt 1000 C  -10 Volt R1 Vin Diketahui : Vref = -9Volt R, R1, R2 ??? Masukan Vin Transduser panas kelvin 00 K  0 Volt 2730 K  2,73 Volt

Perhitungan gain Masukan Vin Transduser panas kelvin 00 K  0 Volt Per 0 K  0,01 Volt diinginkan Keluaran V0 00 C  0 Volt 1000 C  -10 Volt diinginkan per 0 C  0,1 Volt Gain  10 kali

Perhitungan R1 dan R Gain  10 kali Bila R1 =10 KΩ  maka R = 100 KΩ – + Vo R -9 V Vin R1 Gain  10 kali Bila R1 =10 KΩ  maka R = 100 KΩ

Penentuan R2 Tegangan masukan : Diinginkan Keluaran V0 00 C  2730 K = 2,73 Volt Maka Vin =2,73 Volt Diinginkan Keluaran V0 00 C  0 Volt

Hasil Akhir R1=10 KΩ R = 100 KΩ R2 =32727,27 Ω – + Vo R -9 V R1=10 KΩ R = 100 KΩ R2 =32727,27 Ω Vin R1 Persoalannya, bagaimana realisasi R2 ? Pakai hambatan variabel (potensio), agar aman Pot + R tetap. Misal  pot : 10 K dan R = 27 K

VALIDASI R1=10 KΩ R = 100 KΩ R2 =32727,27 Ω Saat suhu 1000 C Maka  R2 – + Vo R -9 V Vin R1 R1=10 KΩ R = 100 KΩ R2 =32727,27 Ω Saat suhu 1000 C Maka  masukan = 3730 K Tegangan Vin = 3,73 V

INTEGRATOR Bila vi konstan maka Linier I1 = (Vi - V)/R1 I2 = set I1 = I2, (Vi - V)/R1 = but V- = V+ = 0 Vi/R1 = Solve for Vo Output is the integral of input signal. CR1 is the time constant Bila vi konstan maka Linier

OUTPUT INTEGRATOR (dengan tegangan masukan tetap) v0 -VCC

APLIKASI Pembangkitan bentuk gelombang Kemiringan tergantung besarnya RC

DIFERENSIATOR R C – Vin + Vo Output is the differential of input signal. CR is the time constant Bila input konstan maka  tegangan output = nol

Aplikasi diferensiator Kelengkungan tergantung besarnya RC

Gelombang gigi gergaji Gelombang kotak Gelombang segitiga PEMBANGKIT FUNGSI Gelombang gigi gergaji Gelombang kotak Gelombang segitiga Gelombang sinus

Pembangkit gelombang gigi gergaji Saklar ditutup sebelum opamp jenuh, kemudian langsung buka lagi I1 I2 Saat saklar ditutup t v0 -VCC

ASTABLE MULTIVIBRATORS PEMBANGKIT GELOMBANG KOTAK A switching oscillator known as Astable Multivibrator can be formed by adding an RC feedback network to a Schmitt Trigger circuit. They are useful to generate low frequency square waves. The comparator and feedback resistor form an inverting Schmitt Trigger having threshold levels of A/2 and –A/2 assuming A is the output level of the comparator. Graphs from Prentice Hall

Astable multivibrators II The operation of the Astable Multivibrators can be described as follows: at time 0, the initial voltage on the capacitor is 0, assuming the initial output voltage is +A (A is the level of the comparator output). Thus, initially the capacitor is charged through the resistor R toward +A. However, when the capacitor voltage reaches A/2, the output voltage rapidly switches to –A. Then the capacitor starts to discharge, once the voltage drops below –A/2, the output again switches back to A. Thus, the capacitor voltage cycles back and forth between A/2 and –A/2. Voltage across capacitor resembles Triangular wave and comparator output voltage is symmetrical square wave.

Astable multivibrators III The period and frequency of the output square waveform can be determined by analyzing the transient response of the RC feedback network. The frequency of oscillation for the Astable Multivibrator shown before is In real circuit design, several non-idealities related to the comparator can affect the frequency, such as the propagation delay of the comparator and bias current effects. To minimize the bias current effects, we usually need to make sure that the smallest current charging to the capacitor should be much larger than the bias current, for example, a few hundred times.

Pembangkit gelombang segitiga Bagaimana memutar knob suatu generator fungsi dapat mengubah frekuensi ? Rangkaian ini terdiri atas integrator, Schmitt trigger dan transistor. Vin

PEMBANGKIT SINUS

Wien Bridge Oscillator Berbasis pada op amp Kombinasi R dan C dlm feedback sehingga factor f tergantung frekuensi. Analisis beranggapan opamp ideal. Gain A sangat besar Arus masuk sangat kecil. Terminal input short. Analyze like a normal feedback amplifier. Determine input and output loading. Determine feedback factor. Determine gain with feedback. Shunt-shunt configuration. R2 R1 V0 Vi ZS If ZP

Wien Bridge Oscillator V0 Vi ZS If ZP Input Loading Output Loading ZS ZS Z1 V0 = 0 Z2 Vi = 0 ZP ZP

Wien Bridge Oscillator Amplifier gain including loading effects R2 R1 V0 Vi If IS Z2 Z1 Feedback factor ZS If V0 ZP

Wien Bridge Oscillator Oscillation condition Loop Gain

Wien Bridge Oscillator - Example Oscillator specifications: o=1x106 rad/s

Wien Bridge Oscillator Final note: No input signal is needed. Noise at the desired oscillation frequency will likely be present and when picked up by the oscillator, it will start the oscillator and the output will quickly buildup to an acceptable level.

Wien Bridge Oscillator Once oscillations start, a limiting circuit is needed to prevent them from growing too large in amplitude

Phase Shift Oscillator Rf If IC3 V2 IC2 V1 IC1 VX C C C V0 R R IR2 IR1 Based on op amp using inverting input Combination of R’s and C’s in feedback loop so get additional 180o phase shift. Analysis assumes op amp is ideal.

Phase Shift Oscillator Rf IC3 IC2 IC1 V2 V1 VX C C C R R IR1 V0 IR2 Example Oscillator specifications: ωo=1x106 rad/s Note: We get 180o phase shift from op amp since input is to inverting terminal and another 180o from the RC ladder.

Summary of Oscillator Design Telah ditunjukkan komponen reaktif di loop feedback dapat menimbulkan osilasi. Agar dicapai feedback posistip. Dengan pemilihan hambatan yang tepat bisa dipilih sinyal feedback yang sefase dengan sinyal input. Dapat dihasilkan amplitude sinusoidal yang besar Telah dijelaskan dua rangkaian oskilator: (Osilator Wien Bridge) (Osilator Geser Fase) untuk menghasilkan frekuensi tertentu, nilai resistor dan kapasitor dihitung berdasarkan persamaan yang ada Catatan akhir: Perancangan osilator semata-mata tergantung pada rangkaian feedback bukan pada karakteristik opamp. Osilator Wien Bridge Osilator Geser Fase

FILTER

Passive Low-Pass Filter ws Vout Vin The pass-band is from 0 to some frequency wp. Its stop-band extends form some frequency ws, to infinity. In practical circuit design, engineers often choose amplitude gain of 0.95 for passive RC filters: C R Vout Vin RL

Design of Passive Filters C R Vout Vin RL The amplitude response: The amplitude gain: Transfer Function The 3dB break-point is at:

Design of Low Pass Active Filters - + Vin Vout R1 RF A B C2 Transfer Function: The -3 dB cut-off frequency: The DC gain: Example: Design a low pass filter with cut-off frequency of 5kHz, and DC gain of 10: Two equations, three unknowns

Design of High Pass Active Filters The -3 dB cut-off frequency: The DC gain: Two equations, three unknowns Select one component based on other conditions, and determine the values of the other two components. Vout - + Vin R1 RF A B C1 Transfer Function: