ICS844S42I Datasheet, PDF (22/27 Pages) Integrated Device Technology – On-chip crystal oscillator for reference frequency generation

ICS844S42I Data Sheet
DUAL OUTPUT RF FREQUENCY SYNTHESIZER
3. Calculations and Equations.
The purpose of this section is to calculate the power dissipation for the LVPECL output pairs.
LVPECL output driver circuit and termination are shown in Figure 8.
V_DDO
Q1
V_OUT
RL
50Ω
V_DDO - 2V
Figure 8. LVPECL Driver Circuit and Termination
To calculate worst case power dissipation into the load, use the following equations which assume a 50 load, and a termination voltage of
V_DDO – 2V.
• For logic high, V_OUT = V_{OH_MAX} = V_{DDO_MAX} – 0.8V
(V_{DDO_MAX} – V_{OH_MAX}) = 0.8V
• For logic low, V_OUT = V_{OL_MAX} = V_{DDO_MAX} – 1.4V
(V_{DDO_MAX} – V_{OL_MAX}) = 1.4V
Pd_H is power dissipation when the output drives high.
Pd_L is the power dissipation when the output drives low.
Pd_H = [(V_{OH_MAX} – (V_{DDO_MAX} – 2V))/R_L] * (V_{DDO_MAX} – V_{OH_MAX}) = [(2V – (V_{DDO_MAX} – V_{OH_MAX}))/R_L] * (V_{DDO_MAX} – V_{OH_MAX}) =
[(2V – 0.8V)/50] * 0.8V = 19.2mW
Pd_L = [(V_{OL_MAX} – (V_{DDO_MAX} – 2V))/R_L] * (V_{DDO_MAX} – V_{OL_MAX}) = [(2V – (V_{DDO_MAX} – V_{OL_MAX}))/R_L] * (V_{DDO_MAX} – V_{OL_MAX}) =
[(2V – 1.4V)/50] * 1.4V = 16.8mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 36mW
ICS844S42BKI REVISION A FEBRUARY 21, 2012
22
©2012 Integrated Device Technology, Inc.