TLV5590 Datasheet, PDF (9/16 Pages) Texas Instruments – 2-BIT ANALOG-TO-DIGITAL CONVERTER FOR FLEX

TLV5590
t 2-BIT ANALOG-TO-DIGITAL CONVERTER
FOR FLEX PAGER CHIPSET
SLAS134B – NOVEMBER 1995 – REVISED NOVEMBER 1996
PRINCIPLES OF OPERATION
digital control
There are five digital inputs that control the TLV5590, along with the CLK input. The five signals are BW, CON1,
CON2, TRACKINH and TEST. All digital control inputs are latched internally on the falling edge of the CLK input.
The BW input selects the cut-off frequency of the input signal third-order Butterworth switched-capacitor filter.
The CON1 and CON2 inputs determine when the TLV5590 is in tracking fast, tracking slow, hold, or low-power
standby mode. In test mode the CLK input is level sensitive, and in all other modes the CLK input is
edge-sensitive.
Table 1 lists the functions for the five control inputs.
Table 1. Control Inputs Function Table
BW
Low
High
CON1
Low
Low
High
High
CON2
Low
High
Low
High
TRACKINH
Low
High
SWITCHED-CAPACITOR FILTER
(– 3 dB POINT)
1-kHz filter cutoff
2-kHz filter cutoff
MODE
Low-power standby (off) mode
Fast track mode
Hold mode
Slow track mode
RESULT
Tracking enabled
Tracking disabled
track inhibit
The TRACKINH input enables the counters to the peak and valley detector DACs. When enabled, the counters
are adjusting to create a DAC output that is the same as the filtered input-signal peak and valley. The counters
decay at the fast or slow decay rates while the TRACKINH input is held low. The TRACKINH line should be
connected to SYMCLK terminal on the TLV5591.
analog-to-digital conversion
The TLV5590 employs a 2-bit ADC to convert a 4-level analog signal to digital data. The digital output is
presented on EXTS0 and EXTS1 with EXTS0 being the LSB. The peak and valley DACs provide the maximum
and minimum voltages (V_ref+ and V_ref–) to the ADC. The input to the 2-bit ADC is the output of the Butterworth
low-pass filter, FILOUT, as shown in the block diagram. The ADC transfer function is shown in Table 2.
Table 2. Filter Output Voltage Selection (see Note 4)
EXTS1 EXTS0
FILTER OUTPUT VOLTAGE (FILOUT)
Low
Low FILOUT < ((peak – valley) x 50/256) + valley
High Low ((peak – valley) x 50/256) + valley < FILOUT < ((peak – valley) x 134/256) + valley
High High ((peak – valley) x 134/256) + valley < FILOUT < (( peak – valley) x 217/256) + valley
Low High FILOUT > ((peak – valley) x 217/256) + valley
NOTE 4. The constants 50/256, 134/256, and 217/256 have a ± 5% tolerance.
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