witam mam bardzo pilna potrzebe przet³umaczenia tekstu o wzmacniaczach izolacyjnych:
THEORY OF OPERATION The ISO122 isolation amplifier uses an input and an output section galvanically isolated by matched 1pF isolating capacitors built into the plastic package. The input is dutycycle modulated and transmitted digitally across the barrier. The output section receives the modulated signal, converts it back to an analog voltage and removes the ripple component inherent in the demodulation. Input and output sections are fabricated, then laser trimmed for exceptional circuitry matching common to both input and output sections. The sections are then mounted on opposite ends of the package with the isolating capacitors mounted between the two sections. The transistor count of the ISO122 is 250 transistors. MODULATOR An input amplifier (A1, Figure 1) integrates the difference between the input current (VIN/200kW) and a switched ?100mA current source. This current source is implemented by a switchable 200mA source and a fixed 100mA current sink. To understand the basic operation of the modulator, assume that VIN = 0.0V. The integrator will ramp in one direction until the comparator threshold is exceeded. The comparator and sense amp will force the current source to switch; the resultant signal is a triangular waveform with a
50% duty cycle. The internal oscillator forces the current source to switch at 500kHz. The resultant capacitor drive is a complementary duty-cycle modulation square wave. DEMODULATOR The sense amplifier detects the signal transitions across the capacitive barrier and drives a switched current source into integrator A2. The output stage balances the duty-cycle modulated current against the feedback current through the
200kW feedback resistor, resulting in an average value at the VOUT pin equal to VIN. The sample and hold amplifiers in the output feedback loop serve to remove undesired ripple voltages inherent in the demodulation process. BASIC OPERATION SIGNAL AND SUPPLY CONNECTIONS Each power supply pin should be bypassed with 1mF tantalum capacitors located as close to the amplifier as possible. The internal frequency of the modulator/demodulator is set at 500kHz by an internal oscillator. Therefore, if it is desired to minimize any feedthrough noise (beat frequencies) from a DC/DC converter, use a p filter on the supplies (see Figure
4). ISO122 output has a 500kHz ripple of 20mV, which can be removed with a simple two pole low-pass filter with a
100kHz cutoff using a low cost op amp. See Figure 4. The input to the modulator is a current (set by the 200kW integrator input resistor) that makes it possible to have an input voltage greater than the input supplies, as long as the output supply is at least ?15V. It is therefore possible when using an unregulated DC/DC converter to minimize PSR related output errors with ?5V voltage regulators on the isolated side and still get the full ?10V input and output swing. An example of this application is shown in Figure
- CARRIER FREQUENCY CONSIDERATIONS The ISO122 amplifier transmits the signal across the isolation barrier by a 500kHz duty cycle modulation technique. For input signals having frequencies below 250kHz, this system works like any linear amplifier. But for frequencies above 250kHz, the behavior is similar to that of a sampling amplifier. The signal response to inputs greater than 250kHzperformance curve shows this behavior graphically; at input frequencies above 250kHz the device generates an output signal component of reduced magnitude at a frequency below 250kHz. This is the aliasing effect of sampling at frequencies less than 2 times the signal frequency (the Nyquist frequency). Note that at the carrier frequency and its harmonics, both the frequency and amplitude of the aliasing go to zero.
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