AFE5808A_15 Datasheet, PDF (34/83 Pages) Texas Instruments – Ultrasound Analog Front-End

AFE5808A
SLOS729D – OCTOBER 2011 – REVISED NOVEMBER 2015
INPUT1
INPUT2
ACT1
IN1
INM1
LNA1
ACT2
IN2
INM2
LNA2
500Ω
Mixer Clock 1
500Ω
500Ω
Mixer Clock 2
500Ω
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Cext
CW_AMPINM
10Ω
10Ω
CW _AMPINP
Rint/Rext
I/V Sum
Amp
Rint/Rext
CW_OUTP
CW_OUTM
Cext
CW I or Q CHANNEL
Structure
INPUT8
ACT8
IN8
INM8
LNA8
500Ω
Mixer Clock 8
500Ω
Note: the approximately 10-Ω to 15-Ω resistors at CW_AMPINM/P are due to internal IC routing and can create slight
attenuation.
Figure 64. Complete In-Phase or Quadrature Phase Channel
The CW mixer in the AFE5808A device is passive and switch based; passive mixer adds less noise than active
mixers. The CW mixer achieves good performance at low power. Figure 65 and Equation 1 describe the
principles of mixer operation, where Vi(t), Vo(t), and LO(t) are input, output and local oscillator (LO) signals for a
mixer respectively. The LO(t) is square-wave based and includes odd harmonic components as shown in
Equation 1.
Vi(t)
Vo(t)
LO(t)
Figure 65. Block Diagram of Mixer Operation
Vi(t) = sin(w₀t + w_dt + j)+ f (w₀t)
LO(t)
=
4
p
éêë_{sin (w0 t ) +}
1
3
sin (3w₀ t ) +
1
5
sin (5w₀ t )...^ùúû
Vo(t)
=
2
p
éëcos ₍w_dt
+
f)-
cos (2w₀ t
-
w_dt
+
f)...ùû
(1)
34
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