AMG-SO204 Datasheet, PDF (5/30 Pages) alpha microelectronics gmbh – Optical Switch IC

AMG-SO204
Optical Switch IC
4. Block Diagram
IN
RF
REFEXT
VDD
Supply
4.5...6.5V
Bandgap
3.3V
CB3V3
VDDA
VREF
Vbg
1.8V
Vref
Bandgap ^Vbg _Vbg
2.5V
Supply Block
Bias IBias
Currents
Vbg
2.5V
VDDD
Logic
Block
OA1EN
OA1
A
Vref
D
ADC1
C
IBias
I
7,2k
OA2
N
ADC2
T
OA3
E
R
ADC3
F
A
GAIN
ADCx3
C
E
Signal Processing Block
OA1EN
GAIN
IO Block
VDDD
2
GNDD
VDDD
4
GNDD
VDDD
4
GNDD
CB3V3
9
GNDD
CB3V3
2
EN ^GNDD
INCLK
EXTINP
RESIN
COMRXD
NPN
EXTCOVER
CPURXD
COMTXD
EXTOUT[1:0]
LIGHTOUT
CPUTXD
ROW[7:0]
SEG[7:0]
LIGHTCURRENT
CBGAIN
VGAOUT
GNDA
GNDD
Figure 2: Block Diagram
5. Block Descriptions
5.1. Current-to-Voltage Converter (OA1)
The converter is built around operational amplifier OA1. Its trans resistance is defined by the
resistance of an off-chip resistor connected between the pins IN and RF of the IC. The DC
voltage applied to the non-inverting input of OA1, which is about 0.5V, defines the average
voltage at the output of the converter. This reference voltage is also available at pin REFEXT
of the IC.
The current to voltage converter can also be built using an external operational amplifier. In
such a case OA1 is disabled by bringing its output to a high-impedance state. This makes it
possible for the output of an external operational amplifier to be connected directly to pin RF. It
is important to remember that, if an external amplifier is used, the voltage at pin RF must not
exceed 2.75V (see Section 6).
5.2. Variable Gain Amplifier (OA2)
The variable gain amplifier is built around operational amplifier OA2. Its gain can be modified
using a 3-bit signal GAIN. The gain can be set to one of six predefined values: 9, 17, 33, 65,
129, and 257V/V. The DC gain of the amplifier is always equal to 1V/V, and the low 3-dB
frequency is set by an external capacitor connected to pin CBGAIN.
AMG-SO204 Revision: A
29. Jul. 2010 © All rights reserved Page 5 of 30