MAXQ7667AACM/V+T【PDF 10/40 页】IC MCU-BASED DAS 16BIT 48-LQFP

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MAXQ7667

16-Bit, RISC, Microcontroller-Based,

Ultrasonic Distance-Measuring System

______________________________________________________________________________________

Sigma-Delta ADC

The MAXQ7667 features a 16-bit sigma-delta ADC with

an analog gain adjustable from 38dB to 60dB (includ-

ing the fixed LNA gain) with a maximum gain step of

12.5% (typical). Gain changes settle within one ADC

conversion. Use software to create a virtual time vari-

able gain amplifier. A digital bandpass and lowpass fil-

ters remove switching glitches and DC offset at the

output of the ADC.

In a typical application, the software sets the gain to a

low value when the burst is first sent and increases the

gain as the time from when the burst was sent increas-

es. As a result, strong echoes from nearby objects are

processed without clipping while small signals from dis-

tant objects are processed with the maximum gain. The

ADC samples the amplified echo signal from the LNA at

80 times the burst output frequency. The ADC provides

conversion results at a data rate equal to 10 times the

burst output frequency. The ADC conversion results

also load to an 8-deep first-in-first-out (FIFO) at the

native data rate or a separate time base without loading

the CPU.

Digital Bandpass Filter

The digital bandpass filter has a center frequency that

tracks the burst output frequency. The bandpass width

is 14% of the center frequency. The bandpass filter pro-

vides the 16-bit output data at a data rate equal to 10

times the burst output frequency.

Full-Wave Rectifier

The full-wave rectifier detects the envelope of the digital

bandwidth filter output to generate a DC output propor-

tional to the peak-to-peak amplitude of the input signal.

Full-wave rectification allows the digital lowpass filter to

respond faster without excessive ripple.

Digital Lowpass Filter

The lowpass filter removes the ripple from the full-wave

detector output. The output of the lowpass filter is avail-

able at a data rate equal to five times the burst output

frequency. The corner frequency is 1/5 the burst fre-

quency with approximately 40dB per decade rolloff.

The 16-bit output data of the lowpass filter is stored in a

FIFO register with a depth of eight samples. The

MAXQ7667 allows data transfer from the lowpass filter

SARC[2:0]:SARS[2:0]

SARC[11:9]:SARMX[2:0]

REFERENCE TO

SIGMA-DELTA ADC

ADC DATA

READY INTERRUPT

ASR.0:SARRDY

APE.12:BGE

APE.14:RBUFE

AIE.0:SARIE

BANDGAP

REF

SARC.3:SARBY

SARC.6:SARDUL

SARC.4:SARASD

SARC.7:SARBIP

SARC.8:SARDIF

OSCC[3:2]:SARCD[1:0]

ADC

CLOCK

DIV

TIMER 0

TIMER 1

TIMER 2

APE.4:SARE

ADCCLK

AVDD

VREF

MUX

SARC[11:9]:SARMX[2:0]

12-BIT

ADC

AIN0

MUX

AIN1

AIN2

AIN3

DATA BUS[15:0]

AIN4

VREF

AGND

AVDD

AGND

REFBG

ADCCTL

REF

SYSCLK

BUF

x1.0

Figure 3. SAR ADC Block Diagram

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