SA5217 Datasheet, PDF (7/12 Pages) NXP Semiconductors – Postamplifier with link status indicator

Philips Semiconductors
Postamplifier with link status indicator
Product specification
SA5217
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Threshold vs R_THRESH for Different Values of R_HYST
(Driven Single Ended)
45
V_CC = 5V
40
T_A = 27_°C
2k
F = 60MHz
35
3k
30
4k
On/Off Voltage vs R_THRESH (Driven Single Ended)
50
V_CC = 5V
40
T_A = 27_°C
F = 60MHz
R_HYST = 4k
30
ON
20
25
5k
10
OFF
6k
20
0
10
20
30
40
50
15
10
20
30
40
50
R_THRESH (kΩ)
R_THRESH (kΩ)
Hysteresis and Forward Active Region
Hysteresis vs R_THRESH for Different Values of R_HYST
(Driven Single Ended)
16
V_CC = 5V
14 ^TA ^{= 27}°^C
5
R_THRESH = 33kΩ
V_IN1
R_HYST = 4kΩ
4
OFF
F = 60MHz
12
10
2k
3k
8
4k 5k
V_THR
3
FORWARD
ACTIVE
2
REGION
(shaded)
6
6k
4
2
10
20
30
40
50
1
0N
0
0
V_HYS
5
10
15
20
25
30
R_THRESH (kΩ)
V_IN (mV_P-P)
SD00358
Figure 5. Typical Performance Characteristics (cont)
THEORY OF OPERATION AND APPLICATION
The SA5217 postamplifier is a highly integrated chip that provides
up to 60dB of gain at 60MHz, to bring mV level signals up to TTL
levels.
The SA5217 contains eight amplifier blocks (see Block Diagram).
The main signal path is made up of a cascade of limiting stages: A1,
A2 and A8. The A3-A4-A7 path performs a wideband full-wave
rectification of the input signal with adjustable hysteresis and decay
times. It outputs a TTL High on the “FLAG” output (Pin 5) when the
input is below a user adjustable threshold. An on-chip LED driver
turns the external LED to the On state when the input signal is
above the threshold. In a typical application the “FLAG” output is
tied back tot he “JAM” input; forcing the “JAM” input to TTL High will
latch the TTL Data Out at the last logical state.
Threshold voltage and hysteresis voltage range are adjustable with
resistors R_THRESH and R_HYST. The typical values given in the data
sheet will result in performance shown in the graph “Hysteresis and
Forward Active Region”. A minority of parts may be sensitive
enough that FLAG High (Off) occurs below the minimum functional
input signal level, V_IN1. This condition is shown by the dotted line in
the graph. Such parts may require adjustment of R_THRESH if it is
important to guarantee that an output signal is present for the full
hysteresis range. If this is not important, R_THRESH may be adjusted
to give a FLAG Low for lower level input signals.
An auto-zero loop allows the SA5217 to be directly connected to a
transimpedance amplifier such as the SA5210, SA5211, or
SA5212A without coupling capacitors. This auto-zero loop cancels
the transimpedance amplifier’s DC offset, the SA5217 A1 offset, and
the data-dependent offset in the PIN diode/transimpedance amplifier
combination.
A typical application of the SA5217 postamplifier is depicted in
Figure 6. The system uses the SA5211 transimpedance amplifier
which has a 28k differential transimpedance gain and a -3dB
bandwidth of 140MHz. this typical application is optimized for a
50Mb/s Non Return to Zero (NRZ) bit stream.
As the system’s gain bandwidth product is very high, it is crucial to
employ good RF design and printed circuit board layout techniques
to prevent the system from becoming unstable.
1998 Oct 07
7