Trusignal
Microelectronics
Integrated Analog Front-End for
TS9514
APRIL 2014 - REVISED AUGUST 2014
Heart Rate Monitors and Low-Cost Pulse Oximeters
Features
•
•
•
•
•
•
Fully-Integrated Analog Front-End for Pulse
Oximeter Applications
Receiver:
High Accuracy Current to Frequency Converter
up to 500KHz
Transmitter:
Flexible Pulse Sequencing and Timing Control
with Integrated LED Driver (H-Bridge)
95dB Dynamic Range
LED Currents Programmable with an External
Resistor and Analog Input Voltages
Power Supplies: 2.5V to 5.5V
Low Power: 1.25 mA at 3.3V Supply
Specified Temperature Range: -40° to +85°
C
C
Package: TSSOP14, QFN16
Applications
•
•
Low-Cost Medical Pulse Oximeter Applications
Optical HRM
Product Description
The TS9514 is a fully-integrated analog front-end
(AFE) that is ideally suited for pulse Oximeter
applications. The device consists of a low-noise I/F
converter and a LED transmitter section. The I/F
converter converts photodiode current to frequency
signal. The LED transmitter currents can be easily
controlled through analog input voltages. The
TS9514’s flexibility allows users to have complete
control of the device’s timing characteristics. The
TS9514 is an AFE solution in TSSOP14 and QFN16
packages and is specified over the operating
temperature from -40° to +85°
C
C.
VDD=2.5V~5.5V
PVDD=2.5V~5.5V
U1
U2
PVDD
VDD
C1
0.1uF
OUT
RED_CS
IR_CS
R1
IN
C3
100uF
C2
0.1uF
ANOD
IR
MCU
R2
RED_REF
RED
R3
GND
IR_REF
NC
PROG
RPROG
4Ω
REV KY.1.0.4
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Ordering Information
Product
TS9514EQR
TS9514ETR
Package-Lead
QFN16
TSSOP14
Package Option
Tape and Reel
Tape and Reel
Package Qty.
2500
2500
TS9514
APRIL 2014 - REVISED AUGUST 2014
Operating Temperature Range
-40° to +85
°
C
C
-40° to +85
°
C
C
Absolute Maximum Ratings
Over operating free-air temperature range, unless otherwise noted.
Value
VDD to GND
Input current to any pin except
supply pins
Momentary
Input current
Continuous
Operating temperature range
Storage temperature range
Maximum junction temperature,
TJ
Human body
model (HBM)
Electrostatic
Machine model
discharge
(MM)
(ESD) ratings
Charge device
model(CDM)
±
10
-40 to +85
–65 to +150
+125
±
2000
±
200
±
500
mA
°
C
°
C
°
C
V
V
V
2.5 to 5.5
±
10
±
50
Unit
V
mA
mA
ESD CAUTION
ESD (electrostatic discharge) sensitive device.
Charged devices and circuit boards can
discharge without detection. Although this
product features patented or proprietary
protection circuitry, damage may occur on
devices subjects to high energy ESD.
Therefore, proper ESD precautions should be
taken to avoid performance degradation or loss
of functionality.
PIN Configuration
15
ANOD
14
PVDD
TS9514
OUT
RED_REF
IR_REF
NC
RED_CS
IR_CS
GND
1
2
3
4
5
6
7
14
13
12
11
10
9
8
IN
ANOD
OUT
1
2
3
4
16
IN
TS9514
13
VDD
12
RED
11
IR
10
PROG
9
VDD
RED_REF
PVDD
IR_REF
IR
RED
PROG
NC
NC
5
6
7
RED_CS
IR_CS
GND
TSSOP14
QFN16
REV KY.1.0.4
2
NC
8
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Microelectronics
TS9514
APRIL 2014 - REVISED AUGUST 2014
Table 1. PIN Descriptions
NO.
（TSSOP14）
1
2
3
4
5
6
7
8
9
10
11
12
13
14
NO.
（QFN16）
1
2
3
4,8,9
5
6
7
10
12
11
14
13
15
16
Name
OUT
RED_REF
IR_REF
NC
RED_CS
IR_CS
GND
PROG
RED
IR
PVDD
VDD
ANOD
IN
Function
Output
Input
Input
Input
Input
Input
Supply
I/O
Output
Output
Supply
Supply
Input
Input
Description
Frequency output
RED LED driver reference voltage input
IR LED driver reference voltage input
No connection pin
RED LED control input. High active
IR LED Control Input. High active
Supply ground pin
LED driver current program pin, connect a resistor to
this Pin
RED LED drive output
IR LED drive output
LED driver power supply pin
Power supply pin
Current input, connect to PIN diode anode
Current input, connect to PIN diode cathode
REV KY.1.0.4
3
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Electrical Characteristics
Minimum and maximum specification are at
TA=-40° to +85°
Typical specifications are at
+25°
C
C.
C.
All specifications are at VDD=3.3V, unless otherwise noticed.
Parameter
Performance (Full-Signal Chain)
V
DD
PV
DD
I
DD
PRF
Receiver supply voltage
LED driver supply voltage
Supply current
Pulse repetition frequency
1
TS9514
APRIL 2014 - REVISED AUGUST 2014
Test Conditions
Min
Typ
Max
Unit
0° to +85
°
C
C
-40° to +85
°
C
C
2.5
2.7
2.5
5.5
5.5
5.5
1.25
1.7
1000
V
V
V
mA
SPS
T
A
=25° VDD=5.5V
C,
I-F Transimpedance Amplifier
f
O
Output frequency
Full-scale frequency
Nonlinearity
R
e
PSRR
Transmitter
Full-scale output current
V
CONTROL
Analog input voltage
Output current offset
Transmitter noise dynamic
range, over 0.1Hz to 5Hz
bandwidth
Minimum on time of LEDs
LED current linearity vs analog
input voltage
Output current settling time
Temperature
Specified temperature range
Storage temperature range
-40
-65
+85
+150
℃
℃
Percent of full-scale current
From 0 to 50 mA
From 50 mA to 0
V
DD
=5V,R
PROG
=4Ω
At 5mA output current
At 25mA output current
At 50mA output current
1
I
IN
=1uA
500
f
O
=0 to 100kHz
100
1000
±
1%
100
kHz
kHz
%FS
kHz/A
%/V
Current responsivity
Power-supply rejection ratio
f
O
=100kHz
0.3
T
A
=25° V
DD
=5V, R
PROG
=4Ω;
C,
V
CONTROL
=0.8V
0
200
V
DD
-2
0.25
TBD
TBD
TBD
50
1%
TBD
TBD
1.25
mA
V
mA
dB
dB
dB
µs
µs
µs
1. The Maximum LED output current depends on PV
DD
, R
PROG
resistance and LED forward voltage strongly; it can be smaller than the
full-scale current.
REV KY.1.0.4
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Overview
The TS9514 is a complete analog front-end (AFE)
circuit targeting pulse oximeter applications. The
device consists of a low-noise I/F converter and a LED
transmitter section. The I/F converter converts the
photodiode current to frequency signal precisely. The
output of the device connects directly to a high
resolution timer of the external microcontroller (MCU)
for which an A/D converter is not necessary. The LED
transmitter current can be adjusted through analog
input voltages.
TS9514
APRIL 2014 - REVISED AUGUST 2014
Figure 1. Timing of LED Control.
Receiver
The
receiver
consists
the
of
a
high
precision
current
to
LED Current Control
The output currents of the transmitter are controlled by
the analog input voltages and are given by the
following equation:
current-to-frequency (I/F) converter section. The I/F
converter
converts
photodiode
frequency signal with high dynamic range and linearity.
The converter continuously converts input current to
frequency without being interrupted by the LED
control signals.
where V
REF
is the voltage at RED_REF or IR_REF pin.
The voltages at RED_REF pin and IR_REF pin control
the RED LED current and IR LED current respectively
and independently.
Transmitter Section
The transmitter section integrates a voltage controlled
constant current source, an H-bridge LED driver and
its control logic. Two LED driver schemes are
supported: an H-bridge drive for a two-terminal
back-to-back LED package and a push-pull drive for a
three-terminal LED package. The on-off of the LED
current is controlled by logic signals at the input pins
of RED_CS and IR_CS, and each LED current can be
adjusted by the corresponding analog input voltage
independently. An external resistor R
PROG
at the
PROG pin sets the ratio of the input voltage to the
LED current and the maximum output current is
primarily dependent on R
PROG
, the power supply
voltage PV
DD
, and the forward voltage of the LEDs.
Timing Diagram of the Transmitter
Figure 1 shows the timing diagram for the LED
transmitter control. Through the internal logic, signals
at the RED_CS and IR_CS pins control the switches
of the H-Bridge. In T1 and T3 cycles, both LEDs are
turned off. In T2 and T4 cycles, RED LED and IR LED
are turned on respectively. Both of the RED_CS and
IR_CS pins are active ‘high’, however, when both are
high at the same time, there will be no current flow
through the two-terminal back-to-back packaged
LEDs (see Table 2 and Table 3).
REV KY.1.0.4
5
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