AD604
MEDICAL ULTRASOUND TGC DRIVING THE
AD9050, A 10-BIT, 40 MSPS ADC
The AD604 is an ideal candidate for the time gain control (TGC)
amplifier that is required in medical ultrasound systems to limit
the dynamic range of the signal that is presented to the ADC.
in a typical medical ultrasound application.
The gain is controlled by means of a digital byte that is input to
an
DAC that outputs the analog gain control signal.
The output common-mode voltage of the AD604 is set to VPOS/2
by means of an internal voltage divider. The VOCM pin is
bypassed with a 0.1 μF capacitor to ground.
The DSX output is optionally filtered and then buffered by
an
op amp, a low distortion, low noise amplifier. The
op amp output is ac-coupled into the self-biasing input of an
ADC that is capable of outputting 10 bits at a 40 MSPS
sampling rate.
0.1µF
1
2
0.1µF
–DSX1
+DSX1
PAO1
FBK1
PAI1
COM1
COM2
PAI2
FBK2
VGN1
24
VREF
23
OUT1
22
GND1
21
VPOS
20
VNEG
19
VNEG
18
VPOS
17
GND2
16
OUT2
15
VOCM
14
VGN2
13
1kΩ
0.1µF
0.1µF
0.1µF
0.1µF
OPTIONAL
FILTER
+5V
0.1µF
–5V
0.1µF
2
3
(MSB) D9
15
AD9050
1kΩ
1kΩ
VREF
OUT
VREF
IN
COMP
REF
BP
AINB
4
5
D8
16
D7
17
D6
18
D5
19
D4
24
D3
25
D2
26
D1
27
V
DD 20
V
DD
22
A/D
OUTPUT
0.1µF
J2
ANALOG
INPUT
50Ω
50Ω
3
4
5
6
7
8
9
AD9631
–IN
OUT
+IN
6
6
0.1µF
9
3
10
AIN
13
ENCODE
14
OR
(LSB) D0
28
0.1µF
10
PAO2
11
+DSX2
12
–DSX2
0.1µF
AD604
100Ω
CLK
1
2
3
V
OUT
B
V
OUT
A
V
SS
V
OUT
C
20
V
OUT
D
19
V
DD 18
A0
17
A1
16
WR
15
DB0
14
(LSB)
DB1
13
DB2
12
DB3
11
+15V
VREF
4
V
REF
5
6
AD7226
AGND
DGND
DB7
7
(MSB)
8
DB6
9
DB5
10
DB4
DIGITAL GAIN CONTROL
Figure 52. TGC Circuit for Medical Ultrasound Application
Rev. D | Page 22 of 32
00540-051
AD [ ANALOG DEVICES ]
