SM9501A/B

NIPPON PRECISION CIRCUITS INC.—9

Crystal Filter Circuit

External crystals are used as filters. Multiple frequencies (40kHz and 60kHz) are supported by connecting

crystals in parallel. The center frequency and bandwidth of the filters is determined by the crystal characteris-

tics. If the center frequency is lower than the target frequency, C

×40 and C×60 can be added to change the res-

onant frequency. And R

×40 and R×60 can be added to adjust the filter Q factor. Internally, pin XO is linked to

pin XI by a phase-inverted signal passed through a capacitor, which cancels the high-frequency components

that pass through the crystal parallel capacitances.

Detector Circuit

The amplified signal is full-wave rectified and passed through a lowpass filter detector. The detector output is

input to peak hold (pin CP) and bottom hold (pin CB) circuits to form the decoder reference potentials and

peak hold potential for AGC control.

Decoder Circuit

The detector output and peak/bottom hold mid-level potential reference are used to decode the time code sig-

nal, which is output on pin OUT. The output is active-LOW, so that the output is LOW when the input ampli-

tude is HIGH.

Standby Function

When PON is open (or HIGH), the device is in standby mode and the current consumption is reduced. Receiver

operation starts when PON goes LOW.

PON

Mode

OUT

Open (or HIGH)

Standby

HIGH

LOW

Operating

Time code

XO

Rx40

Rx60

Cx40

Cx60

40kHz

60kHz

XI

Amplifier

Rectifier

LPF

Peak/

Bottom

Hold

Bottom hold

Peak hold

Bottom hold

Peak hold

Mid-level potential

Decoder

OUT output

LPF waveform

Rectifier

LPF

Peak/

Bottom

Hold