M02050_17 Datasheet, PDF (19/28 Pages) M/A-COM Technology Solutions, Inc. – 3.3/5V Limiting Amplifier for Applications to 2.5 Gbps

Applications Information
4.1.1
Reference Current Generation
The M02050-15 contains an accurate on-chip bias circuit that requires an external 12.1 kΩ 1% resistor, R_REF, from
pin I_REF to ground to set the LOS threshold voltage at ST_SET precisely.
Figure 4-2. Reference Current Generation
V_CC3
R_ST
ST_SET
V_SET
V_{LVL_Det}
LOS
BG_Ref
R_REF
I_REF
4.1.2
Connecting V_CC and V_CC3
For 5V operation, the V_CC pin is connected to an appropriate 5V ± 7.5% supply. No potential should be applied to
the V_CC3 pin. The only connection to V_CC3 should be R_ST as shown in Figure 3-5.
When V_CC = 5V all logic outputs and the data outputs are 5V compatible while the CML data inputs are still refer-
enced to 3.3V from the internal regulator (see Figure 3-2). For low power operation, V_CC and V_CC3 should be con-
nected to an appropriate 3.3V ± 7.5% supply. In this case all I/Os are 3.3V compatible.
4.1.3
Choosing an Input AC-Coupling Capacitor
When AC-coupling the input the coupling capacitor should be of sufficient value to pass the lowest frequencies of
interest, bearing in mind the number of consecutive identical bits, and the input resistance of the part. For SONET
data, a good rule of thumb is to chose a coupling capacitor that has a cut-off frequency less than 1/(10,000) of the
input data rate. For example, for 2.5 Gbps data, the coupling capacitor should be chosen as:
f_CUTOFF ≤ (2.5x10⁹ / 10x10³) = 250x10³
The -3 dB cutoff frequency of the low pass filter at the 50 Ω input is found as:
02050-DSH-002-F
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