VCA2613Y BURR-BROWN [Burr-Brown Corporation], VCA2613Y Datasheet - Page 12

• Manufacturer Part Number: VCA2613Y
• Description: Dual, VARIABLE GAIN AMPLIFIER with Low-Noise Preamp
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

comparator input threshold, the VCA output is blocked and
an appropriate fixed DC level is substituted, providing fast
and clean overload recovery. The basic architecture is shown
in Figure 14. Both high and low overrange conditions are
sensed and corrected by this circuit.
FIGURE 14. Overload Protection Circuitry.
Figures 15 and 16 show typical overload recovery wave-
forms with MGS = 100, for VCA + PGA minimum gain (0dB)
and maximum gain (36dB), respectively. LNP gain is set to
25dB in both cases.
FIGURE 15. Overload Recovery Response For Minimum Gain.
12
FIGURE 13. Programmable Attenuator Section.
–
INPUT
VCM
E
A
B1
B2
From VCA
E
A
Comparators
VCA
R
E = Maximum Peak Amplitude
CNTL
S
A1
= 0.2V, DIFFERENTIAL, MGS = 100, (0dB)
Q
Selection
1A
Logic
200ns/div
Q
1B
A2
Q
2A
PGA
Output
Input
Gain = A
PROGRAMMABLE ATTENUATOR SECTION
Output
Q
2B
www.ti.com
A3
Q
INPUT OVERLOAD RECOVERY
One of the most important applications for the VCA2613 is
processing signals in an ultrasound system. The ultrasound
signal flow begins when a large signal is applied to a
transducer, which converts electrical energy to acoustic
energy. It is not uncommon for the amplitude of the electrical
signal that is applied to the transducer to be 50V or greater.
To prevent damage, it is necessary to place a protection
circuit between the transducer and the VCA2613, as shown
in Figure 17. Care must be taken to prevent any signal from
turning the ESD diodes on. Turning on the ESD diodes inside
the VCA2613 could cause the input coupling capacitor (C
to charge to the wrong value.
FIGURE 16. Overload Recovery Response For Maximum Gain.
FIGURE 17. VCA2613 Diode Bridge Protection Circuit.
3A
VCA
Q
Protection
3B
Network
CNTL
= 3.0V, DIFFERENTIAL, MGS = 100, (36dB)
A4
Q
4A
200ns/div
C
F
Q
V
4B
DD
LNP
ESD Diode
IN
A5
P
R
F
LNP
Q
Output
5A
Input
VCA2613
SBOS179D
LNP
OUTPUT
OUT
Q
N
5B
C
)