6.2
BD4000 Analogue Section
US/FECG Input
, balanced signals from the ultrasound transducer are fed into the
differential amplifier which converts them to single ended mode.
The US signal is then low-pass filtered and fed to the FMD section for further
filtering/amplification and also to the high-pass filter.
This bandpass filtered signal is then level controlled then boosted to drive the speaker.
It is also fed through a sharp low-pass anti-alias filter before arriving at the AGC input.
This DAC based stage allows the micro to regulate the ultrasound signal before
sampling.
US Timing Logic
, the master oscillator for the ultrasound system is also located on the
main PCB analogue section.
This 1.5MHz carrier is first amplified before being fed to the ultrasound transducer and
the rear connector PCB.
The timing logic controlled by the micro sets the ultrasound transmit timing and fully
synchronises the system in the twins ultrasound mode.
FECG
, the FECG leg plate output signal is low-pass filtered then fed to the AGC
circuit. In FECG mode the ultrasound signal is disabled and the AGC used to regulate
the FECG signal amplitude before sampling.
An unfiltered version of the FECG leg plate output signal is also fed to the micro and
sampled.
Issue: 2 DRAFT
19
Rev: a
614365
Power
Amplifier
Anti Alias
Filter
AGC
Micro-
controller
Volume
Control
Low Pass
Filter
FMD
Band Pass
Filter
US/FECG
Input
Transducer
Type Detect
Gain
Control
US
Differential
Amplifier
FECG
Low Pass
Filter
RF
Amplifier
1.5MHz
SYNC/Gate
SYNC/
Gate
Osc
US
Timing
Logic
Serial Ports
TOCO /
IUP Input
Transducer
Type Detect
Differential
Amplifier
FECG Wideband
