CS48L32 datasheet(37/192 Pages) CIRRUS

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DS1219F4

Cirrus Logic

CS48L32

4.2 Input Signal Path

R47112 (0xB808)

US1_DET_

CONTROL

30:28 US1_DET_DCY[2:0]

000

Ultrasonic Detect 1 Decay Time Constant

Time period (after the hold time, and in the absence of valid detections) for the

accumulated count to decrease to 37% of its previous value.

The quoted times are valid for US1_FREQ = 010; if US1_FREQ = 011, the

time period is multiplied by 0.84.

000 = 0 ms

001 = 0.79 ms

010 = 1.58 ms

011 = 3.16 ms

100 = 6.33 ms

101 = 12.67 ms

110 = 25.34 ms

111 = 50.69 ms

27:24 US1_DET_HOLD[3:0]

0000

Ultrasonic Detect 1 Hold Time

The number of invalid detections required before the accumulated count

decreases is 2(X+4) – 1, where X is US1_DET_HOLD in integer coding and

X > 0. If US1_DET_HOLD = 0, the hold time is 0. The detection frequency is

set by US1_FREQ.

0000 = 0

0001 = 31

0010 = 63

0011 = 127

...

1101 = 131071

1110 = 262143

1111 = 524287

23:20 US1_DET_NUM[3:0]

0000

Ultrasonic Detect 1 Accumulator Count Threshold

Accumulated number of detections threshold is 2X, where X is US1_DET_

NUM in integer coding. The detection frequency is set by US1_FREQ.

0000 = 1

0001 = 2

0010 = 4

0011 = 8

...

1101 = 8192

1110 = 16384

1111 = 32768

18:16 US1_DET_THR[2:0

000

Ultrasonic Detect 1 Signal Level Threshold

000 = –6 dBFS

001 = –9 dBFS

010 = –12 dBFS

011 = –15 dBFS

100 = –18 dBFS

101 = –21 dBFS

110 = –24 dBFS

111 = –27 dBFS

6:5

US1_DET_LPF_

CUT[1:0]

Ultrasonic Detect 1 Low-pass Filter Control

Selects the cut-off frequency of the low-pass filter, dependent on US1_FREQ.

If US1_FREQ = 010 the low-pass filter is set as follows:

00 = 1722 Hz, 01 = 833 Hz, 10 = 408 Hz, 11 = 203 Hz

If US1_FREQ = 011 the low-pass filter is set as follows:

00 = 2044 Hz, 01 = 989 Hz, 10 = 484 Hz, 11 = 241 Hz

US1_DET_LPF

Ultrasonic Detect 1 Low-pass Filter Enable

0 = Disabled

1 = Enabled

R47124 (0xB814)

US2_CONTROL

13:12 US2_GAIN[1:0]

Ultrasonic Demodulator 2 Gain

00 = Disabled (no signal)

01 = –5 dB

10 = 1 dB

11 = 7 dB

11:8 US2_SRC[3:0]

0x0

Ultrasonic Demodulator 2 Source

0x0 = IN1L

0x1 = IN1R

0x2 = IN2L

0x3 = IN2R

All other codes are reserved

6:4

US2_FREQ[2:0]

011

Ultrasonic Demodulator 2 Frequency

010 = 16–24 kHz

011 = 20–28 kHz

All other codes are reserved

Table 4-7. Ultrasonic Signal-Detect and Demodulation Control (Cont.)

Bit

Label

Default

Description

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