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AD2S80A датащи(PDF) 10 Page - Analog Devices |
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AD2S80A датащи(HTML) 10 Page - Analog Devices |
10 / 20 page AD2S80A –10– CIRCUIT FUNCTIONS AND DYNAMIC PERFORMANCE The AD2S80A allows the user greater flexibility in choosing the dynamic characteristics of the resolver-to-digital conversion to ensure the optimum system performance. The characteristics are set by the external components shown in Figure 1, and the section “COMPONENT SELECTION” explains how to select desired maximum tracking rate and bandwidth values. The following paragraphs explain in greater detail the circuit of the AD2S80A and the variations in the dynamic performance avail- able to the user. Loop Compensation The AD2S80A (connected as shown in Figure 1) operates as a Type 2 tracking servo loop where the VCO/counter combination and Integrator perform the two integration functions inherent in a Type 2 loop. Additional compensation in the form of a pole/zero pair is required to stabilize any Type 2 loop to avoid the loop gain characteristic crossing the 0 dB axis with 180 ° of additional phase lag, as shown in Figure 5. This compensation is implemented by the integrator compo- nents (R4, C4, R5, C5). The overall response of such a system is that of a unity gain second order low pass filter, with the angle of the resolver as the input and the digital position data as the output. The AD2S80A does not have to be connected as tracking con- verter, parts of the circuit can be used independently. This is particularly true of the Ratio Multiplier which can be used as a control transformer (see Application Note). A block diagram of the AD2S80A is given in Figure 3. Ratio Multiplier The ratio multiplier is the input section of the AD2S80A and compares the signal from the resolver input angle, θ, to the digital angle, φ, held in the counter. Any difference between these two angles results in an analog voltage at the AC ERROR OUTPUT. This circuit function has historically been called a “Control Transformer” as it was originally performed by an electromechanical device known by that name. The AC ERROR signal is given by A1 sin ( θ–φ) sin ωt where ω = 2 π fREF fREF = reference frequency A1, the gain of the ratio multiplier stage is 14.5. So for 2 V rms inputs signals AC ERROR output in volts/(bit of error) = 2 × sin 360 n × A1 where n = bits per rev = 1,024 for 10 bits resolution = 4,096 for 12 bits = 16,384 for 14 bits = 65,536 for 16 bits giving an AC ERROR output = 178 mV/bit @ 10 bits resolution = 44.5 mV/bit @ 12 bits = 11.125 mV/bit @ 14 bits = 2.78 mV/bit @ 16 bits The ratio multiplier will work in exactly the same way whether the AD2S80A is connected as a tracking converter or as a con- trol transformer, where data is preset into the counters using the DATA LOAD pin. HF Filter The AC ERROR OUTPUT may be fed to the PSD via a simple ac coupling network (R2, C1) to remove any dc offset at this point. Note, however, that the PSD of the AD2S80A is a wide- band demodulator and is capable of aliasing HF noise down to within the loop bandwidth. This is most likely to happen where the resolver is situated in particularly noisy environments, and the user is advised to fit a simple HF filter R1, C2 prior to the phase sensitive demodulator. The attenuation and frequency response of a filter will affect the loop gain and must be taken into account in deriving the loop transfer function. The suggested filter (R1, C1, R2, C2) is shown in Figure 1 and gives an attenuation at the reference frequency (fREF) of 3 times at the input to the phase sensitive demodulator . Values of components used in the filter must be chosen to ensure that the phase shift at fREF is within the allowable signal to reference phase shift of the converter. Phase Sensitive Demodulator The phase sensitive demodulator is effectively ideal and devel- ops a mean dc output at the DEMODULATOR OUTPUT pin of ±22 π × (DEMODULATOR INPUT rms voltage ) PHASE SENSITIVE DEMODULATOR A1 sin ( – ) sin t AC ERROR sin sin t cos sin t DIGITAL VCO R5 R6 C5 C4 R4 INTEGRATOR VELOCITY CLOCK DIRECTION RATIO MULTIPLIER Figure 3. Functional Diagram REV. C |
Аналогичный номер детали - AD2S80A_15 |
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Аналогичное описание - AD2S80A_15 |
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