AD604
Rev. E | Page 22 of 32
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.
Figure 52 shows a schematic of an AD604 driving an AD9050
in a typical medical ultrasound application.
The gain is controlled by means of a digital byte that is input to
an AD7226 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 AD9631 op amp, a low distortion, low noise amplifier. The
op amp output is ac-coupled into the self-biasi ng input of an
AD9050 ADC that is capable of outputting 10 bits at a 40 MSPS
sampling rate.
20
27
28
26
22
14
13
10
15
16
17
18
19
24
25
3
4
9
6
5
AD9050
COMP
VREFIN
VREFOUT
REFBP
AINB
D8
D5
D6
D7
D4
D3
ENCODE
OR
AIN D2
D1
(LSB)D0
VDD
13
16
15
14
18
17
24
23
22
21
20
19
12
11
10
9
8
7
1
2
3
4
6
5
AD604 1kΩCLK
J2
12
11
20
19
18
17
16
15
14
13
10
9
8
1
2
3
4
7
6
5
AD7226
AGND
VREF
VSS
DGND
DB6
DB5
DB4
A1
A0
DB1
DB2
DB3
VREF
+15V
DIGITAL GAIN CONTROL
FILTER
2
AD9631
3
6
OPTIONAL
–IN
–DSX1
+DSX1
PAI1
FBK1
PAO1
COM1
VGN1
VREF
VPOS
GND1
OUT1
VNEG
1kΩ1kΩ
0.1µF
0.1µF
ANALOG
INPUT
0.1µF
0.1µF
A/D
OUTPUT
(MSB)D9
+IN
OUT
COM2
PAI2
FBK2
PAO2
+DSX2
–DSX2
VNEG
VPOS
GND2
OUT2
VOCM
VGN2
50Ω
50Ω
100Ω
VDD
0.1µF
0.1µF
0.1µF
0.1µF0.1µF0.1µF
DB7
(MSB)
VOUTA
VOUTBV
OUTC
VOUTD
VDD
DB0
(LSB)
WR
00540-051
+5V
0.1µF
–5V
0.1µF