X9470 Datasheet, PDF (13/25 Pages) Xicor Inc. – RF Power Amplifier (PA) Bias Controller

Preliminary Information
X9470
Figure 2. Sense and Scale Block Diagram
INC/DEC
RW_REF RH_REF RL_REF ^VOUT
V_DD
V_SENSE+ ^RSENSE
V_SENSE–
I_DQ
Cint~2pF ±10%
∆V
V_REF
10kΩ
64-tap
Comparator
INC/DEC
K₂ = 20X
~1kohm
K₁ = 50X
Precision
I-Amp
RF
choke
PA
Out
V_gate
RF PA in
The wiper of the digital potentiometer acts like its
mechanical equivalent and does not move beyond the
last position. That is, the counter does not wrap around
when clocked to either extreme. The electronic
switches in the potentiometer operate in a “make
before break” mode when the wiper changes tap posi-
tions. If the wiper is moved several positions, multiple
taps are connected to the wiper for t_IW (SCL to
RW_BIAS change).
When the device is powered-up, the X9470 will load
the last saved value from the non-volatile memory into
the WCR. Note that the current wiper position can be
saved into non-volatile memory register by using the
SCL and CS pins as shown in Figure 4.
Important note: the factory setting of the wiper counter
register is the ZERO-position (0 of 255 taps). This is
the default wiper position.
Bias Adjustment Block Instructions and Program-
ming. The SCL, INC/DEC (internal signal) and CS
inputs control the movement of the wiper along the
resistor array. (See Table 1) With CS set HIGH, the
device is selected and enabled to respond to the INC/
DEC and SCL inputs. HIGH to LOW transitions on SCL
will increment or decrement R_BIAS (depending on the
state of the INC/DEC input). The INC/DEC input is
derived from the output of the comparator of the Sense
and Scale Block.
Storing Bias Resistor Values in Memory. Wiper val-
ues are stored to VOLATILE memory automatically
when CS is HIGH and INC/DEC either transitions from
HIGH to LOW or from LOW to HIGH. Wiper values are
stored to NON-VOLATILE memory during Byte Write
or as described in the following section.
Table 1. Mode Selection
INC /
SDA CS* SCL DEC
Mode
H
H
H VBIAS is incremented
one tap position.
H
H
L VBIAS is decremented
one tap position.
H
H
X
Lock Wiper Position.
or Save to volatile
memory. (BiasLock™)
X
L
X
X Open Loop.
* When coming out of shutdown, the CS pin must be cycled once before bias
adjustment is enabled.
REV 11.16 3/20/03
www.xicor.com
13 of 25