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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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AD73322AST датащи(PDF) 32 Page - Analog Devices |
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AD73322AST датащи(HTML) 32 Page - Analog Devices |
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32 / 43 page  AD73322 –32– REV. B Interfacing to an Electret Microphone Figure 34 details an interface for an electret microphone which may be used in some voice applications. Electret microphones typically feature a FET amplifier whose output is accessed on the same lead which supplies power to the microphone, there- fore this output signal must be capacitively coupled to remove the power supply (dc) component. In this circuit the AD73322 input channel is being used in single-ended mode where the internal inverting amplifier provides suitable gain to scale the input signal relative to the ADC’s full-scale input range. The buffered internal reference level at REFOUT is used via an external buffer to provide power to the electret microphone. This provides a quiet, stable supply for the microphone. If this is not a concern, then the microphone can be powered from the system power supply. CONTINUOUS TIME LOW-PASS FILTER VREF VFBN1 VINN1 VINP1 VFBP1 VOUTP1 VOUTN1 REFCAP REFOUT AD73322 VREF +6/–15dB PGA REFERENCE 0/38dB PGA GAIN 1 C1 R2 R1 C2 RB RA +5V ELECTRET PROBE 10 F CREFCAP Figure 34. Electret Microphone Interface Circuit Analog Output The AD73322’s differential analog output (VOUT) is produced by an on-chip differential amplifier. The differential output can be ac-coupled or dc-coupled directly to a load which can be a headset or the input of an external amplifier (the specified mini- mum resistive load on the output section is 150 Ω.) It is possible to connect the outputs in either a differential or a single-ended configuration but please note that the effective maximum output voltage swing (peak to peak) is halved in the case of single- ended connection. Figure 35 shows a simple circuit providing a differential output with ac coupling. The capacitors in this cir- cuit (COUT) are optional; if used, their value can be chosen as follows: C fR OUT C LOAD = 1 2 π where fC = desired cutoff frequency. VFBN1 GAIN 1 VREF VINN1 VINP1 VFBP1 VOUTP1 VOUTN1 REFCAP REFOUT REFERENCE AD73322 CREFCAP RLOAD COUT COUT +6/–15dB PGA CONTINUOUS TIME LOW-PASS FILTER Figure 35. Example Circuit for Differential Output Figure 36 shows an example circuit for providing a single-ended output with ac coupling. The capacitor of this circuit (COUT) is not optional if dc current drain is to be avoided. VFBN1 GAIN 1 VREF VINN1 VINP1 VFBP1 VOUTP1 VOUTN1 REFCAP REFOUT REFERENCE AD73322 RLOAD COUT 0.1 F +6/–15dB PGA CONTINUOUS TIME LOW-PASS FILTER Figure 36. Example Circuit for Single-Ended Output Differential to Single-Ended Output In some applications it may be desireable to convert the full differential output of the decoder channel to a single-ended signal. The circuit of Figure 37 shows a scheme for doing this. VFBN1 GAIN 1 VREF VINN1 VINP1 VFBP1 VOUTP1 VOUTN1 REFCAP REFOUT REFERENCE AD73322 VREF 0/38dB PGA RLOAD R I R I R F R F 0.1 F +6/–15dB PGA CONTINUOUS TIME LOW-PASS FILTER Figure 37. Example Circuit for Differential to Single- Ended Output Conversion |
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