Rainbow-electronics MAXQ7667 Manual do Utilizador descarregar pdf (Página 17)

MAXQ7667

Echo Receive Path

Low-Noise Amplifier (LNA)

The LNA provides a 40V/V fixed gain to the input signal.

The differential inputs of the LNA are ECHOP and

ECHON. For proper biasing of the LNA, AC-couple the

transducer or any external circuitry to ECHOP and

ECHON. For a single-ended input signal, AC-couple the

signal to ECHOP with a 0.01µF capacitor and connect

ECHON to AGND through a 0.01µF capacitor placed as

close as possible to the signal source. The outputs of the

LNA connect to the inputs of a 16-bit sigma-delta ADC

and can connect internally to the AIN0 and AIN1 inputs

of the SAR ADC for external monitoring (Figure 2).

Diagnostic Signals

An analog multiplexer located at the input of the LNA

selects one of three possible signals for processing by

the echo receive path; the normal echo signal AC-cou-

pled to the ECHOP and ECHON inputs, 0V signal, or a

2mV

P-P

internally generated signal (Figure 2). The

2mV

P-P

square-wave signal, with frequency and duty

cycle matching the burst signal, allows the echo

receive chain to process a simulated echo.

MAXQ7667

0.47µF

AGND

REFGB

0.47µF

TO EXTERNAL VOLTAGE

REFERENCE

AGND

REF

VARIABLE

GAIN SIGMA-

DELTA ADC

FIFO

8 x 16

FIFO

CONTROL

BANDPASS

FILTER

CLOCK

CONTROL

ECHO

RECEIVE

CLOCK

RCVC[4:0]:RCVGN[4:0]

RCVC[7:6]:LNAISEL[1:0]

RCVC.8:LNAOSEL

BPFI[15:0]

APE.13:RSARE

2.5V

BANDGAP REF

APE.12:BGE

FULL-WAVE

RECTIFIER PLUS

LOWPASS FILTER

*R = ECHO INPUT RESISTANCE. SEE THE ELECTRICAL CHARACTERISTICS SECTION.

40R*

AIN0

TO SAR ADC

AIN1

2mV

P-P

40R*

LNA

AVDD/2

ECHOP

ECHON

MUX

BPFO[15:0]

LPFD[15:0]

CMPC[14:0]:CMPH[14:0]

CMPT[15:0]

LPFC[15:12]:FFIL[3:0]

LPFC[2.0]:FFLS[2:0]

LPFC.7:FFOV

ASR.2:LPFFL

LPFC[11:8]:FFDP[3:0]

CMPC.15:CMPP

ASR.12:CMPLVL

AIE.3:CMPIE

LPFF[15:0]

ASR.3:CMPI

COMPARATOR

AIE.1:LPFIE

ASR.1:LPFRDY

LPFC.3:FFLD

TIMER 0

TIMER 1

TIMER 2

DATA READY

INTERRUPT

AIE.2:LFLIE

Figure 2. Echo Receive Path

16-Bit, RISC, Microcontroller-Based,

Ultrasonic Distance-Measuring System

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MAXQ7667 1

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