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LTC6602

6602fc

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Dual Matched, High

Frequency Bandpass/Lowpass Filters

The LTC

6602 is a dual, matched, programmable bandpass

or lowpass ﬁlter and differential driver. The selectivity of the

LTC6602, combined with its phase matching and dynamic

range, make it ideal for ﬁltering in RFID systems. With two

degree phase matching between channels, the LTC6602 can

be used in applications requiring highly matched ﬁlters,

such as transceiver I and Q channels. Gain programmabil-

ity, and the fully differential inputs and outputs, simplify

implementation in most systems.

Both channels of the LTC6602 consist of a programmable

lowpass and highpass ﬁlter. For bandpass functionality,

the lowpass ﬁlters are programmed for the upper cutoff

frequency. For lowpass functionality, the highpass ﬁlters

can be bypassed. The ﬁlter cutoff frequencies can be set

with a guaranteed accuracy of 3% with the use of a single

resistor. Alternatively, the ﬁlter cutoff frequencies can be

controlled with an external clock.

The LTC6602 operates on a single 2.7V to 3.6V supply

and features a low power shutdown mode.

UHF RFID Reader Dual Baseband Filter and Dual ADC

Matched Dual Filter/Driver, Ideal for RFID Readers

Guaranteed Phase Matching to Within 2 Degrees

Guaranteed Gain Matching to Within 0.2dB

Conﬁgurable as Lowpass or Bandpass:

– Programmable 5th Order Lowpass: 42kHz to 900kHz

– Programmable 4th Order Highpass: 4.2kHz to 90kHz

Programmable Gain: 1×, 4×, 16×, 32×

Simple Pin Programming or SPI Interface

Low Noise: –145dBm/Hz (Input Referred)

Low Distortion: –75dBc at 200kHz

Differential, Rail-to-Rail Inputs and Outputs

Input Range Extends from 0V to 5V

Low Voltage Operation: 2.7V to 3.6V

Shutdown Mode

4mm × 4mm QFN Package

Multiprotocol RFID Readers: EPC-GEN2, ISD and IPX

IDEN, PHS, GSM Basestations

Repeaters, Radio Links, and Modems

Wireless Telemetry

JTRS

6602 TA01

LTC6602

V+

+INA

–INA

+INB

–INB

BIAS

OCM

MUTE

GAIN0(D0)

GAIN1

GND

–OUTA

+OUTA

–OUTB

+OUTB

CLKIO

SER

CLKCNTL

HPF0(SDO)

HPF1(SDI)

LPF0(SCLK)

LPF1(CS)

V+

MUTE

INPUT

FROM

TRANSMITTER

38.3k

0.1µF

LTC2297

CLK IN

0.1µF

CS SCLK SDI

SPI CONTROL INPUT

I INPUT

Q INPUT

I OUTPUT

Q OUTPUT

2.2µF

–

÷4

CLOCK INPUT

24MHz TO 128MHz

(COVERS THE TAG BACKSCATTER LINK FREQUENCY RANGE OF 40kHz to 640kHz

OF THE CLASS 1 GENERATION 2 UHF RFID COMMUNICATION PROTOCOL)

100pF

14-BIT

ADC

14-BIT

ADC

100Ω

Gain vs Frequency

FREQUENCY (Hz)

GAIN (dB)

6602 TA01b

–40

–30

–20

–10

–50

–60

1k 1M 10M100k10k

EXTERNAL CLOCK = 90MHz

90kHz-900kHz BPF

15kHz-150kHz BPF

45kHz-300kHz BPF

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

Summary of content (28 pages)

PAGE 1
LTC6602 Dual Matched, High Frequency Bandpass/Lowpass Filters FEATURES n n n n n n n n n n n n n DESCRIPTION Matched Dual Filter/Driver, Ideal for RFID Readers Guaranteed Phase Matching to Within 2 Degrees Guaranteed Gain Matching to Within 0.2dB Configurable as Lowpass or Bandpass: – Programmable 5th Order Lowpass: 42kHz to 900kHz – Programmable 4th Order Highpass: 4.
PAGE 2
LTC6602 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) +OUTA MUTE GAIN0(D0) GAIN1 +INA –INA TOP VIEW V+IN to GND.................................................................6V V+A, V+D to GND..........................................................4V Filter Inputs to GND........................ –0.3V to V+IN + 0.3V All Other Pins to GND............... –0.3V to V+A, V+D + 0.3V Output Short-Circuit Duration...........................
PAGE 3
LTC6602 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+A = V+D = V+IN = 3V, VICM = VOCM = 1.5V, Gain = 0dB, lowpass cutoff = 300kHz, highpass cutoff = 45kHz, internal clocking with RBIAS = 54.9k unless otherwise noted. PARAMETER CONDITIONS Filter Phase Either Channel External Clock = 90MHz, VIN = 3.
PAGE 4
LTC6602 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+A = V+D = V+IN = 3V, VICM = VOCM = 1.5V, Gain = 0dB, lowpass cutoff = 300kHz, highpass cutoff = 45kHz, internal clocking with RBIAS = 54.9k unless otherwise noted. PARAMETER CONDITIONS PGA Gain Lowpass Cutoff = 150kHz, Highpass Filter Bypassed, Measured at DC, 0.6V to 2.
PAGE 5
LTC6602 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+A = V+D = V+IN = 3V, VICM = VOCM = 1.5V, Gain = 0dB, lowpass cutoff = 300kHz, highpass cutoff = 45kHz, internal clocking with RBIAS = 54.9k unless otherwise noted. PARAMETER CONDITIONS Supply Current, Shutdown Mode Sum of the Currents into V+D, V+A, and V+IN; All Supplies Set to 3V Shutdown Via Serial Interface, Control Bit D1 = 1.
PAGE 6
LTC6602 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Specifications apply to pins 6, 9-11, 21 and 22. Pin Programmable Control Mode Specifications SYMBOL PARAMETER CONDITIONS MIN VIH Digital Input High Voltage Pins 6, 9-11, 21, 22 l VIL Digital Input Low Voltage Pins 6, 9-11, 21, 22 l IIN Digital Input Current Pins 6, 9-11, 21, 22 (Note 7) l TYP MAX UNITS V+D = 2.7V to 3.
PAGE 7
0 15-150kHz BPF -10 -20 LTC6602 Gain (dB) TYPICAL PERFORMANCE CHARACTERISTICS -30 -40 Distortion vs Input Frequency 20 –70 15kHz-150kHz BPF 90kHz-900kHz BPF –10 –20 –30 HD3 12kHz-82kHz BPF HD2 45kHz-300kHz BPF –80 –85 –40 HD2 12kHz-82kHz BPF –50 45kHz-300kHz BPF 10k 100k 1M FREQUENCY (Hz) –90 10M 0 50 100 150 200 250 INPUT FREQUENCY (kHz) –70 HD3 HD2 –80 6 12 18 GAIN (dB) 24 HD2 –90 30 15 30 45 60 75 HIGHPASS CUTOFF FREQUENCY (kHz) 0.10 RBIAS = 54.
PAGE 8
LTC6602 TYPICAL PERFORMANCE CHARACTERISTICS Common Mode Rejection 100 GAIN = 12dB GAIN = 0dB 90 80 70 GAIN = 24dB GAIN = 30dB 60 TA = 25°C 50 V = 3V S 40 VIN-CM = 0V ΔVIN-CM = 1.25VP-P 30 RBIAS = 54.9k 15kHz-150kHz BPF 20 1k 10k 100k FREQUENCY (Hz) 120 TA = 25°C, VS = 3V, 110 VIN-CM = 0V, ΔVIN-CM = 1.25VP-P, RBIAS = 54.
PAGE 9
LTC6602 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C VS = 3V RBIAS = 54.9k 105 SUPPLY CURRENT (mA) OUTPUT IMPEDANCE (Ω) Supply Current vs Supply Voltage 110 10 15kHz-150kHz BPF 90kHz-900kHz BPF 1 900kHz LPF CLKCNTL PIN FLOATING RBIAS = 54.9k 45kHz-300kHz BPF GAIN = 0dB 90kHz-900kHz BPF 100 85°C 100 Supply Current vs Temperature 120 SUPPLY CURRENT (mA) Output Impedance vs Frequency 100 25°C –40°C 95 45kHz-300kHz BPF 0.1 1k 10k 100k 1M FREQUENCY (Hz) 90 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.
PAGE 10
LTC6602 PIN FUNCTIONS V+IN (Pin 1): Input Voltage Supply (2.7V ≤ V ≤ 5.5V). This supply must be kept free from noise and ripple. It should be bypassed directly to a ground plane with a 0.1µF capacitor unless it is tied to V+A (Pin 2). The bypass should be as close as possible to the IC, but is not as critical as the bypassing of V+A and V+D (Pin16). V+A (Pin 2): Analog Voltage Supply (2.7V ≤ V ≤ 3.6V). This supply must be kept free from noise and ripple.
PAGE 11
LTC6602 PIN FUNCTIONS CLKIO (Pin 15): When CLKCNTL (Pin 5) is tied to ground, CLKIO is the master clock input. When CLKCNTL is floated, CLKIO is pulled to ground by a weak, 5µA pulldown. When CLKCNTL is tied to V+D (Pin 16), CLKIO is the master clock output. When configured as a clock output, this pin can drive 1k and/or 5pF loads. Heavier loads may cause inaccuracies due to supply bounce at high frequencies. V+D (Pin 16): Digital Voltage Supply (2.7V ≤ V ≤ 3.6V).
PAGE 12
LTC6602 BLOCK DIAGRAM +INA –INA GAIN1 GAIN0(D0) MUTE +OUTA 24 23 22 21 20 19 V+IN 1 18 –OUTA CHANNEL A PGA LPF HPF V+A 2 17 SER CONTROL VDDA BIAS CLK 1.6k VOCM 3 16 V+D 1.
PAGE 13
LTC6602 APPLICATIONS INFORMATION Theory of Operation (Refer to Block Diagram) Pin Programmable Interface The LTC6602 features two matched filter channels, each containing gain control, lowpass, and highpass networks that are controlled by a single control block and clocked by a single clock generator. The gain, lowpass and highpass sections can be independently programmed. The two channels are not independent, i.e. if the gain is set to 24dB, then both channels have a gain of 24dB.
PAGE 14
LTC6602 APPLICATIONS INFORMATION V+D SHUTDOWN OUT 6-BIT GAIN, BW CONTROL CODE 8-BIT LATCH CS HPF0(SDO) Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7 8-BIT SHIFT-REGISTER DIN (INTERNAL NODE) 6602 F02 Figure 2. Bidirectional Design of HPFO(SDO) and GAIN0(D0) Pins 6602 F03 Figure 3. Diagram of Serial Interface (MSB First Out) 3.3V 3.3V 0.1µF V+IN LTC6602 #1 0.
PAGE 15
LTC6602 APPLICATIONS INFORMATION Serial Interface Self-Clocking Operation Connecting SER to ground allows the filter to be controlled through the SPI serial interface. When CS is low, the serial data on SDI is shifted into an 8-bit shift-register on the rising edge of the clock (SCLK), with the MSB transferred first (see Figure 3). Serial data on SDO is shifted out on the clock’s falling edge. A high CS will load the 8 bits of the shift-register into an 8-bit D-latch, which is the serial control register.
PAGE 16
LTC6602 APPLICATIONS INFORMATION are shown in Table 3. When the LTC6602 is programmed for the lowest lowpass cutoff frequency (LPF1, LPF0 = ‘0’), the power is automatically reduced by about 35%. Table 2. Cutoff Frequency Control, RBIAS = 54.9k, fCLK = 90MHz LPF1 LPF0 LOWPASS BW (kHz) HPF1 HPF0 HIGHPASS BW (kHz) 0 0 150 0 0 15 0 1 300 0 1 45 1 0 900 1 0 90 1 1 900 1 1 Bypass HPF LPF1 LPF0 LOWPASS BW (kHz) HPF1 HPF0 HIGHPASS BW (kHz) 0 0 41.175 0 0 4.1175 0 1 82.
PAGE 17
LTC6602 APPLICATIONS INFORMATION Preserving Oscillator Accuracy The oscillator is sensitive to transients on the positive supply. The IC should be soldered to the PC board and the PCB layout should include a 0.1µF ceramic capacitor between V+A (Pin 2) and ground, as close as possible to the IC to minimize inductance. The PCB layout should also include an additional 0.1µF ceramic capacitor between V+D (Pin 16) and ground.
PAGE 18
LTC6602 APPLICATIONS INFORMATION –70 TA = 25°C fIN = 100kHz DIFFERENTIAL INPUT, VIN = 1.5VP-P –75 RBIAS = 54.9k 45kHz-300kHz BPF GAIN = 0dB DISTORTION (dBc) DISTORTION (dBc) –70 HD3 –80 HD2 –85 –90 TA = 25°C fIN = 100kHz DIFFERENTIAL INPUT, VIN = 1.5VP-P –75 RBIAS = 54.9k 45kHz-300kHz BPF GAIN = 0dB HD3 –80 HD2 –85 0 0.5 1.0 1.5 2.0 2.5 COMMON MODE INPUT VOLTAGE (V) –90 3.0 0 1 2 3 4 COMMON MODE INPUT VOLTAGE (V) 6602 F08 6602 F09 Figure 8.
PAGE 19
LTC6602 APPLICATIONS INFORMATION –20 –30 DISTORTION (dBc) VSUPPLY TA = 25°C fIN = 100kHz VIN = 1.5VP-P RBIAS = 54.9k 45kHz-300kHz BPF GAIN = 0dB –40 0.1µF V+A –50 V+D –60 HD3 –70 VIN+ –80 –90 0.5 + – VIN– 1.0 1.5 2.0 2.5 COMMON MODE OUTPUT VOLTAGE (V) 0.1µF RPULL-UP RPULL-UP VIN– 0.1µF 1µF VOUT– GND LTC6602 0.1µF V+IN 1.87k 1.87k –OUTA –INA –OUTB VOCM VIN+ V+D GND 1.87k VIN– + – LTC6602 V+IN V+A 0.1µF +INA 6602 F11 VSUPPLY VSUPPLY V+D + – 1µF V+A 0.
PAGE 20
LTC6602 APPLICATIONS INFORMATION 3.3V 3.3V LTC6602 MASTER 0.1µF V+IN RBIAS V+A V+IN + +INA +OUTA – –INA –OUTA + VOUT1 – RBIAS V+A RBIAS V+D VIN1 LTC6602 SLAVE 0.1µF RBIAS V+D + +INA +OUTA – –INA –OUTA VIN2 CLKCNTL CLKCNTL CLKIO CLKIO GND GND + VOUT2 – 6602 F13 Figure 13. Two Filters in a Master/Slave Configuration If the lowpass cutoff frequency varies then the Figure 12b circuit must be used. The output common mode voltage is equal to the voltage of the VOCM pin.
PAGE 21
LTC6602 APPLICATIONS INFORMATION Mute Function The LTC6602 features a mute function which is asserted by pulling MUTE (Pin 20) to ground. This breaks the signal path that leads from the input pins to the filter networks, attenuating the input signal by at least 20dB. The mute function can be used to protect the filter inputs from large transients. The filter clock continues to run when the filter is muted, allowing for a fast recovery time when MUTE is deasserted.
PAGE 22
LTC6602 APPLICATIONS INFORMATION 120 fCLK (MHz) SUPPLY CURRENT (mA) 100 HPF1 = 0 HPF1 = 0 HPF0 = 0 HPF0 = 1 10 LPF1 = 1 LPF1 = 0 LPF0 = 1 10k 100k FILTER CUTOFF FREQUENCY (Hz) 60 40 20 HPF1 = 1 LPF1 = 0 HPF0 = 0 LPF0 = 0 1k TA = 25°C VS = 3V 100 CLKCNTL PIN FLOATING HPF1 = 0 HPF0 = 1 80 GAIN = 0dB 0 10k 1M LPF1 = 0 LPF0 = 0 LPF1 = 0 LPF0 = 1 LPF1 = 1 100k LOWPASS CUTOFF FREQUENCY (Hz) 6602 F15 1M 6602 F16 Figure 15. fCLK vs Filter Cutoff Frequencies Figure 16.
PAGE 23
LTC6602 APPLICATIONS INFORMATION The LTC6602, an Adaptable Baseband Filter for an RFID Reader A radio-frequency identification (RFID) system is an auto-id technology that identifies any object that contains a coded tag. An RFID system consists of a reader (or interrogator) and a tag. An RFID system capable of identifying multiple tags at a maximum operating distance operates in the UHF frequency range.
PAGE 24
LTC6602 APPLICATIONS INFORMATION detecting the symbol sequence (in an RFID environment, noise will be superimposed on the output signal). In general, increasing the lowpass fCUTOFF and/or decreasing the highpass fCUTOFF “enhances” signal transitions and intervals and increases filter output noise. 5V 3V 0.1µF 1 2 V+IN V+A 24 +INA SPI CONTROL OF DAC SETS THE LTC6602 CLOCK FREQUENCY 40MHz TO 100MHz 1 2 3 16 V+D –OUTA 18 I CHANNEL INPUT 23 –INA 7 +INB Q CHANNEL INPUT CS VOUT SCLK GND SDI 0.
PAGE 25
LTC6602 TYPICAL APPLICATIONS Switching the RBIAS Resistor 3V PARALLEL CONTROL 1 2 V+IN V+A 16 24 +INA –OUTA 18 +OUTA 19 23 –INA 7 +INB 8 4 R3 R2 0.1µF R1 3 20 SOT-363 21 22 14 25 DIODES INC DMN2004DMK CLK1 CLK0 0 0 RBIAS1 0 1 RBIAS2 1 0 RBIAS3 1 1 RBIAS4 RBIAS1 > RBIAS2 OR RBIAS3 fCLK1 fCLK2 fCLK3 fCLK4 CLK1 0.
PAGE 26
LTC6602 PACKAGE DESCRIPTION UF Package 24-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1697) 0.70 ±0.05 4.50 ± 0.05 2.45 ± 0.05 3.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD R = 0.115 TYP 0.75 ± 0.05 PIN 1 NOTCH R = 0.20 TYP OR 0.35 × 45° CHAMFER 23 24 PIN 1 TOP MARK (NOTE 6) 0.40 ± 0.10 1 2 2.45 ± 0.10 (4-SIDES) (UF24) QFN 0105 0.200 REF 0.00 – 0.05 0.25 ± 0.05 0.50 BSC NOTE: 1.
PAGE 27
LTC6602 REVISION HISTORY (Revision history begins at Rev C) REV DATE DESCRIPTION PAGE NUMBER C 10/10 Updated Filter Phase Either Channel Min value for fIN = 125kHz to –143 in Electrical Characteristics section 3 Updated all Max values for Supply Current in Electrical Characteristics section 4 6602fc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 28
LTC6602 TYPICAL APPLICATION Direct Conversion Demodulator and Programmable Baseband Filter RF IN 5V 4.7pF 3V 0.1µF 270nH* 0.1µF 10pF 4 3 2 1 GND GND RF GND 16 5 6 VCC 7 V CC 8 VCC 5V 1µF EN 0.1µF 15 LT5575 270nH* 10pF 270pF 10pF 24 +INA 10pF I INPUT 23 –INA 14 Q INPUT 10pF 1000pF 13 1 V+IN 10pF 7 +INB 8 –INB 4 38.3k 270nH* GND LO GND VCC 17 9 10 11 12 10pF 270nH* 10pF 20 270pF 0.1µF 21 22 1000pF MUTE INPUT FROM TRANSMITTER LO IN 3 4.