TS34118CS

TS34118 TSC | Alldatasheet

Document overview

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Technical content

Features

— Improved attenuator gain range: 52dB between transmit and receive. — Low voltage operation for line-powered applications (3.0-6.5V). — 4-point signal sensing fo r improved sensitivity. — Back ground noise monitors for both transmit and receive paths. — Standard 28-pin plastic DIP package and SOP package available. — Microphone amplifier gain set by external resistors-mute function included. — Chip disable for active/standby operation. — On board filter pinned-out for user defined function. — Dial tone detector to inhibit receive idle mode during dial tone presence. — Compatible with TS34119 speaker amplifier.

Ordering Information

Part No. Operating Temp. Package TS34118CD DIP-28 TS34118CS -20 ~ +70 oC SOP-28 Absolute Maximum Rating Description Value Unit Supply voltage (pin 4) -1.0, +7.0 V Voltage at CD (pin 3), MUT (pin 12) -1.0,Vcc +1.0 V Voltage at VLC (pin 13) -1.0,Vcc +0.5 V Voltage at TXI (pin 9),RXI (pin 21),FI(pin 2) -0.5,Vcc +0.5 V Storage temperature range -65 to +150 oC

TS34118 2-20 2004/09 rev. B Recommended Operating Conditions Description Min. Typ. Max. Units Supply voltage (pin 4) (see Text) 3.5 -- 6.5 V CD input (pin 3), MUT input (pin 12) 0 -- Vcc V IVB current (pin 15) - -- 500 µA VLC (pin 13) 0.3xV B -- V B V Attenuator input signal voltage (pin 9,21) 0 -- 350 mVrms Microphone amplifier, Hybrid amplifier gain 0 -- 40 dB Load current @RXO, TXO (pins 8,22) @MCO (pin 10) @ H T O - , H T O + ( p i n 6 , 5 ) ±2.0 ±1.0 ±5.0 mA Ambient operating temperature range -20 -- +60 ℃ Electrical Characteristics (TA=+25, Vcc=5.0V, CD≤ 0.8V, unless noted) Parameter Symbol Min Typ Max Unit Power Supply Vcc supply current (Vcc=6.5V, CD=0.8V) ( V c c = 6 . 5 V , C D = 2 . 0 V ) Icc -- 5.5 600 8.0 800 mA µA CD input resistance (Vcc=VCD=6.5V) CD input voltage - High - L o w R CD VCDH VCDL 2.0 Vcc 0.8 KΩ V V VB output voltage (Vcc=3.5V) ( V c c = 5 . 0 V ) VB -- 1.8 1.3 2.1 2.4 V VB output resistance (IVB=1.0mA) R OVB -- 400 -- Ω VB power supply rejection ratio (CVB=220µF,f=1.0KHz) PSRR -- 54 -- dB Attenuators (TA=+25℃) Receive attenuator gain (f=1.0KHz, VLC=VB ) Rx model, RXI=150mVrms (Vcc=5.0V) Rx model, RXI=150mVrms (Vcc=3.5V) Gain change –Vcc=3.5V versus Vcc=5.0V AGC gain change –Vcc=2.8V versus Vcc=5.0V* Idle model, RXI=150mVrms Range (Rx to Tx model) G RX GRX ∆GRX1 ∆GRX2 GRX1 ∆GRX3 +4.0 +4.0 -0.5 -22 +6.0 +6.0 -25 -20 +8.0 +8.0 +0.5 -15 -17 dB Volume control range (Rx model, 0.3VB<VLC<VB) VCR 27 35 -- dB RXO DC voltage (Rx model) VRXO -- VB -- V ∆RXO DC voltage (Rx to Tx model) ∆VRXO -- ±10 ±150 mV RXO high voltage (Iout=-1.0mA RXI=VB+1.5V) VRXOH 3.7 -- -- V RXO low voltage (Iout=+1.0mA, RXI=VB-1.0, Output measured with respect to VB)* VRXOL -- -1.5 -1.0 V RXI input resistance (RXI<350mVrms) RRXI 7.0 10 14 K Ω Transmit attenuator gain (f=1.0KHz) Tx model , TXI=150mVrms Idle model, TXI=150mVrms Range (Tx to Rx model) G TX GTXI ∆GTXI +4.0 -22 +6.0 -20 +8.0 -17 dB TXO DC voltage (Tx model) V TXO -- V B -- V ∆TXO DC voltage (Tx to Rx model) ∆VTXO -- ±30 ±150 mV TXO High voltage (Iout=-1.0mA TXI=VB+1.5V) V TXOH 3.7 -- -- V TXO Low voltage (Iout=+1.0mA TXI=VB-1.0V, Output measured with respect to VB)* VTXOL -- -1.5 -1.0 V

TS34118 3-20 2004/09 rev. B Electrical Characteristics (TA=+25, Vcc=5.0V, CD≤ 0.8V, unless noted) Parameter Symbol Min Typ Max Unit Attenuators-continued (TA=+25℃) TXI input resistance (TXI<350mVrms) R TXI 7.0 10 14 K Ω Gain tracking (GRX + GTX, @ Tx, Idle, Rx)* G TR -- ±0.1 -- dB Attenuator Control (TA=+25℃) CT voltage (pin 14-VB) Rx model (V LC=VB) Idle model Tx model V CT +240 -240 mV CT source current(switching to Rx mode) I CTR -85 -60 -40 µA CT sink current(switching to Tx mode) I CTT +40 +60 +85 µA CT slow idle current I CTS -- 0 -- µA CT fast idle internal resistance R FI 1.5 2.0 3.6 K Ω Microphone Amplifier (TA=+25℃,VMUT≤0.8V,AVCL=31dB unless otherwise noted) Output offset (VMCO-VB, feedback R=180KΩ) MCOvos -50 0 +50 mV Open loop gain (f<100Hz) A VOLM 70 80 -- dB Gain bandwidth GBW M -- 1.0 -- MHz Output High voltage (Iout=-1.0mA, Vcc=5.0V) V MCOH 3.7 -- -- V Output Low voltage (Iout=+1.0mA) V MCOL -- -- 200 mV Input bias current (@MCI) I BM -- -40 -- nA Muting (∆Gain) (f=1.0KHz, VMUT=2.0V) (300Hz<f<10KHz) GMT -55 -68 -- dB MUT input resistance (Vcc=VMUT=6.5V) R MUT 50 90 -- K Ω MUT Input-High V MUTH 2.0 -- Vcc V MUT Input-Low V MUTL 0 -- 0.8 V Hybrid Amplifiers (TA=+25 )℃ HTO-offset(VHTO- -VB, Feedback R=51KΩ) H VOS -20 0 +20 mV HTO- to HTO+ offset (Feedback R=51KΩ) HB VOS -30 0 +30 mV Open loop gain(HTI to HTO-, f<100Hz) A VOLH 60 80 -- dB Gain bandwidth GBW H -- 1.0 -- MHz Closed loop gain(HTO- to HTO+) A VCLH -0.35 0 +0.35 dB Input bias current(@HTI) I BH -- -30 -- nA HTO- High voltage (Iout=-5.0mA) V HT-H 3.7 -- -- V HTO- Low voltage (Iout=+5.0mA) V HT-L -- -- 250 mV HTO+ High voltage (Iout=-5.0mA) V HT+H 3.7 -- -- V HTO+ Low voltage (Iout=+5.0mA) V HT+L -- -- 450 mV Distortion(300Hz<f<10KHz, see Figure 1) THD H -- 0.3 -- % Level Detectors and Background Noise Monitors (TA=+25℃) Transmit-Receive switch threshold (Ratio of current at RLI1 + RLI2 to 20µA at TLI1 + TLI2 to switch from Tx to Rx) ITH 0.8 1.0 1.2 Source current at RLO1, RLO2, TLO1, TLO2 I LSO -- -2.0 -- mA Sink current at RLO1, RLO2, TLO1, TLO2 I LSK -- 4.0 -- µA CPR, CPT output resistance (Iout=1.5mA) R CP -- 35 -- Ω CPR, CPT leakage current I CPLK -- -0.2 -- µA Filter (TA=+25℃) Voltage offset at FO (VFO-VB, 220KΩ from VB to FI) FO VOS -200 -90 0 mV FO sink current I FO 150 260 400 µA FI bias current I FI -- -50 -- nA

TS34118 4-20 2004/09 rev. B Electrical Characteristics (TA=+25, Vcc=5.0V, CD≤ 0.8V, unless noted) Parameter Symbol Min Typ Max Unit System Distortion (TA=+25℃, f=1.0KHz) Rx mode (from FI to RXO, FO connected to RXI) THDR -- 0.5 3.0 % Tx mode (from MCI to HTO-/HTO+, includes Tx attenuator) THDT -- 0.8 3.0 % 1. All currents into a device pin are positive, those out of a pin are negative. Algebraic convention rather than magnitude is used to define limits. Simplified Block Diagram Temperature Characteristics Parameter Typical Value @25 ℃ Typical Change –20 to +60 ℃ Vcc supply current (CD=0.8V) 5.0mA -0.3%/ ℃ Vcc supply current (CD=2.0V) 400µA -0.4%/ ℃ VB output voltage (Vcc=5.0V) 2.1V +0.8%/ ℃ Attenuator gain (Max Gain) +6.0dB 0.0008dB/ ℃ Attenuator gain (Max attenuation) -46dB 0.004dB/ ℃ Attenuator input resistance (@ TXI, RXI) 10K Ω +0.6%/ ℃ Dial tone detector threshold 15mV +20µV/ ℃ CT source, sink current ±60µA -0.15%/ ℃ Microphone, Hybrid amplifier offset 0 mV ±4.0µV/ ℃ Transmit-Receive switching threshold 1.0 ±0.02%/ ℃ Sink current at RLO1, RLO2, TLO1, TLO2 4.0µA -10nA/ ℃ Closed loop gain (HTO- to HTO+) 0 dB 0.001%/ ℃

TS34118 5-20 2004/09 rev. B Pin Function Description Pin Name Description 1 FO Filter output. Output impedance is less than 50 ohms. 2 FI Filter input. Input im pedance is greater than 1.0Mohm. 3 CD Chip Disable. A logic low(<0.8V) sets normal operat ion. A logic high (>2.0V) disables the IC to conserve power. Input impedance is norminally 90KΩ. an AGC circuit reduces the receive attenuator gain by ≈25dB (when in the receive mode). 5 HTO+ Output of the second hybrid amplif ier. The gain is internally set at –1.0 to provide a differential output, in conjunction with HTO-, to the hybrid transformer. 6 HTO- Output of the first hybrid amplifier. The gain of the amp is set by external resistors. 7 HTI Input and summing node for the first hybrid amplifier . DC level is ≈VB. 8 TXO Output of the transmit att enuator. DC level is approximately VB. 9 TXI Input to the transmit attenuator. Max. Si gnal level is 350m Vrms . Input impedance is 10KΩ. 10 MCO Output of the microphone amplif ier. The gain of the amplifier is set by external resistors. 11 MCI Input and summing node of the microphone amplifier. DC level is≈ VB.

12 MUT

Mute input. A logic low(<0.8V) sets norma l operation. A logic high (>2.0V) mutes the microphone amplifier without affect ing the rest of the circui t. Input impedance is norminally 90KΩ.

13 VLC

Volume control input. When VLC=V B , the receive attenuator is at maximum gain when in the receive mode. When VLC=0.3V B, the receive gain is down 35dB. Does not affect the transmit mode. 14 C T An RC at this pin sets the response time for the circuit to switch modes. 15 V B An output voltage≈Vcc/2. This voltage is a system ac gr ound, and biases the volume control. A filter cap is required 16 CPT An RC at this pin sets the time c onstant for the transmit background monitor. 17 TLI2 Input to the transmit leve l detector on the mike/speaker side.

18 TLO2 Output of the transmit level detector on the mike/speaker si de, and input to the transmit

background monitor. 19 RLO2 Output of the receive leve l detector on the mike/speaker side. 20 RLI2 Input to the receive leve l detector on the mike/speaker side. 21 RXI Input to the receive attenuator and dial tone detector. Max i nput level is 350mV RMS. Input impedance is ≈10KΩ. 22 RXO Output of the receive att enuator. DC level is approximately VB. 23 TLI1 Input to the transmit level detector on the line side. 24 TLO1 Output of the transmit level detector on the line side.

25 RLO1 Output of the receive level detector on the line side, and i nput to the receive background

monitor. 26 RLI1 Input to the receive level detector on the line side. 27 CPR An RC at this pin sets the time c onstant for the receive background monitor. 28 GND Ground pin for the entire IC.

duplex. The handset is full duplex since con-version can occu r in both directions (transmit and receive) simultaneously. circuit operates in a “hands free” mode, eliminating the need for a “push to talk” switch. against a person’s eat.) oscillations don’t occur. associated functions, please refer to the Block Diagram (Figure 2) when reading the following sections. paths to provide the half-duplex operation required in a speakerphone. impedance is 10Ω until the output current limit typically 2.5mA) is reached. Figure 3. Attenuator Input Stage

The attenuators are controlled by t he single output of the Control Blo ck, which is measurable at the C T pin (pin 14). the most direct method of monitoring the circuit’s mode. Block is given in the section describing the Control Block. Figure 4. Level Detectors

TS34118 10-20 2004/09 rev. B Attenuator Control Block The Attenuator Control Block has the seven inputs described above: -The output of the comparator operated by RLO2 and TLO2 (microphone/speaker side) - designated C1. -The output of the comparator operated by RLO1 and TLO1 (TIP/Ring side) – designated C2. -The output of the transmit background noise monitor – designated C3. -The output of the receive background noise monitor -designated C4. -The volume control. -The dial tone detector. -The AGC circuit. The single output of the Control Block controls the two attenuators. The effect of C1-C4 is as follows: Input Output C1 C2 C3 C4 Mode Tx Tx 1 X Transmit Tx Rx Y Y Fast Idle Rx Tx Y y Fast Idle Rx Rx X 1 Receive Tx Tx 0 X Slow Idle Tx Rx 0 0 Slow Idle Rx Tx 0 0 Slow Idle Rx Rx X 0 Slow Idle X=Don’t Care; y=C3 and C4 are not both 0. A definition of the above terms: 1)”Transmit” means the transmit attenuator is fully on (+ 6.0dB), and the receive attenuat or is at max. attenuation (-46dB). 2)”Receive” means both attenuators are controlled by the volume control. At max. Volume, the receive attenuator is fully on (+6.0dB), and the transmit attenuator is at max. attenuation (-46dB). 3)”Fast Idle” means both transmit and receive speech is pr esent in approximately equal levels. The attenuators are quickly switched (30ms) to idle until one speech level dominates the other. 4)”Slow Idle” means speech has ceased in both transmit and receive paths. The attenuators are then slowly switched (1 second) to the idle mode. 5) Switch to the full transmit or receive modes from any other mode is at the fast rate (≈30ms). A summary of the truth table is as follows: 1)The circuit will switch to transmit if: a) both transmit level detectors sense higher signal levels relative to the respective receive level detectors (TLI1 versus RLI1, TLI2 versus RLI2), and b) the transmit background noise monitor indicates the presence of speech. 2)The circuit will switch to receive if: a) both receive level detectors sense higher signal levels relative to the respective transmit level detectors, and b) the receive background noise monitor indicates the presence of speech. 3) The circuit will switch to the fast idle mode if the level detec tors disagree on the relative strengths of the signal levels, and at least one of the background noise monitors indicates speech. For example, referring to the Block Diagram (Figure 2), if there is suffi cient signal at the microphone amp output (TLI2) to ov erride the speaker signal (RLI2), and there is sufficient signal at the receive input (RLI1) to override t he signal at the hybrid output (TLI1), and either or both background monitors indi cate speech, then the circuit will be in the fast idle mode. Two conditions which can cause the fast idle mode to occur are a) when both talkers are attemp ting to gain control of the system by talking at the same time, and b)when one talker is in a very noisy environment, forcing the other talker to continually override that noise level. In general, the fast idle mode will occur infrequently.

speech level is continuously overridden by noise at the other speaker’s location. -RT is typically 120KΩ, and CT is typically 5.0µF. discharging the capacitor to VB with a time constant = 2.0K×CT. open, and the capacitor discharges to VB through the external resistor RT with a time constant = RT × CT. Figure 6. CT Attenuator Control Block Circuit reached (typically 1.5mA).Input bias current at MCI is typically 40nA out of the pin. be kept within the range of ground and Vcc (see Figure 17). If the mute function is not used, the pin should be grounded.

Figure 9. Low Pass Filter telephone line or a power supply. to the rejection at VB, as well as their respective gains. Depicts this graphically. ground and Vcc . If CD is not used, the pin should be grounded. secondarily by the capacitors at the level detector outputs (RLO1, RLO2, TLO1, TLO2). to transmit (or vice-versa), the total switching time would be 40ms. transmit or receive is described above.

TS34118 14-20 2004/09 rev. B Switching Time If the circuit is switching to “slow idle”, the time constant is determined by the C T capacitor and RT, the external resistor (see Figure 6). With CT = 5.0µF, and RT = 120KΩ, the time constant is ≈600ms, giving a switching time of ≈ 1.8 seconds (for 95% change). The switching period to slow idle begi ns when both speakers have st opped talking. The switching time back to the original mode will depend on how soon that speaker begins speaking agai n. The sooner the speaking time starts during the 1.8 seconds peri od, the quicker the switching time since a smaller voltage excursion is required. That switching time is determined by the internal current sources as described above. The above switching times occur, however, after the level detectors have detected the appropriate signal levels, since their outputs operate the Attenuator Control Block. Referring to Figure 4, t he rise time of the level detector’s outputs to new speech is quick by comparison ( ≈1.0ms), determined by the internal 350 Ωresistor and the external capacitor (typically 2.0µF). The output’s decay time is determined by the external capa citor, and an internal 4.0µF current source giving a decay rate of ≈60ms for 120mV excursion at RLO or TLO. However, the overall response time of the circuit is not a constant since it depends on the relative strength of t he signals at the different leve l detectors, as well as the timing of the signals with respect to each other. The capacitors at the four outputs (RLO1, RLO2, TLO1, TLO2) must be equal value (±10%) to prevent problems in timing and level response. The rise time of the level detector’s out puts is not significant since it is so short. The decay time, however, provides a significant part of the “hold time” necessary to hold the circuit during the normal pauses in speech. The components at the inputs of the level detectors (RLI1, RLI2, TLI1,TLI2) do not affect the switching time, but rather affect the relative signal levels required to switch the circuit, as well as the frequency response of the detectors. Design Equations Referring to Figure 10(the coupling capacitors have been omitted for simplicity), the following definitions will be used (all measurements are at 1.0KHz) -GMA is the gain of the microphone amplifier measured from the microphone output to TXI (typically 35V/V, or 31dB); -GTX is the gain of the transmit attenuator, measured from TXI to TXO; -GHA is the gain of hybrid amplifiers, m easured from TXO to the HTO-/HTO+ diff erential output (typically 10.2V/V, or 20.1dB); -GHT is the gain from HTO-/HTO+ to Tip/Ring for transmi t signals, and includes the bal ance network (measured at 0.4V/V, or –8.0dB); -GST is the side tone gain, measured from HTO-/HTO+ to the filter input (measured at 0.18V/V , or –15dB); -GHR is the gain from Tip/Ring to the filter input for receive signals (measured at 0.833V/V or –1.6dB); -GFO is the gain of the filter stage, measured from the input of the filter to RXI, typically 0dB at 1.0KHz; -GRX is the gain of the receive attenuator measured from RXI to RXO; -GSA is the gain of the speaker amplifier, measured from RXO to the differ ential output of the TS 34119 (typical 22V/V or 26.8dB); -GAC is the acoustic coupling, measured from the speaker differential voltage to the microphone output voltage. I) Transmit Gain The transmit gain, from the microphone output (V M) to tip and Ring, is determined by the output characte ristics of the microphone, and the desired transmit level. For exam ple, a typical electret microphone will produce ≈0.35mVrms under normal speech conditions. To achieve 100mVrms at Tip / Ring, an overall gain of 285V/V is necessary. The gain of the 357V/V is required of the microphone and hybr id amplifiers. It is desirable to hav e the majority f that gain in the microphone amplifier for three reasons: 1) The low level signals from the microphone should be amp lifier as soon as possible to minimize signal/noise problems.

TS34118 15-20 2004/09 rev. B Design Equations 2) To provide a reasonable signal level to the TLI2 le vel detector; and 3)to minimize any gain applied to broadband noise generated within the attenuator. However, to co ver the normal voice band, t he microphone amplifier’s gain should not exceed 48dB. For the circuit of Figure 10, the gain of the microphone amplifier was set at 35V/V (31dB), and the differential gain of the hybrid amplifiers was set at 10.2V/V (20.1dB). II) Receive Gain The overall receive gain depends on the incoming signal leve l, and the desired out put power at the speaker. Normal receive levels (independent of the peaks) at Tip/Ring can be 35mVrms (-27dBm). Although on long lines That level can be down to 8.0mVrms (-40dBm).The speaker power is: PSPK = Rs 0.610dBm/10× (Equation 1) Where RS is the speaker impedance, and the dBm term is the incoming signal level increased by the gain of the receive path. Experience has shown that ≈30dB gain is a satisfactory amount for the majority of applications. Using the above numbers and Equation 1, it would appear that the resulting power to the speaker is extremely low. However, Equation 1 does not consider the peaks in normal s peech, which can be 10 to 15 times the rms value. Considering the peaks, the overall average power approaches 20-30mV on long lines, and much more on short lines. Referring to Figure 10, the gain from Tip/Ring to the filter input was measured at 0.833V/V (-1.6dB), the filter’s gain is unity, and the receive attenuator’s gain is 2.0V/V (+6.0dB) at maximum volume. The speaker amplifier’s gain is set at 22V/V (26.8dB), which puts the overall gain at ≈31.2dB. III) Loop Gain The total loop gain must add up to less than zero dB to obtain a stable circuit. This can be expressed as: GMA+GTX+GHA+GST+GFO+GRX+GSA+GAC<0 (Equation 2) Using the typical numbers ment ioned above, and knowing that G TX+GRX=-40dB, the required acoustic coupling can be determined: An acoustic loss of at least 23 dB is necessary to prevent instability and oscillations, commonly referred to as “singing.” However, the following equations show that greater acoustic loss is necessa ry to obtain proper level detection and switching. IV) Switching Threshold To switch comparator C1, currents I1 and I3 need to be det ermined. Referring to Figure 11, with a receive signal V L applied to Tip/Ring, a current I3 will flow through R3 into RLI2 according to the following equation: I3 = VL ⎥⎦ ⎡ ××× 2 GGGG SA RXFOHR (Equation 4) Where the terms in the brackets ar e the V/V gain terms. The speaker amp lifier gain is divided by two since G SA is the differential gain of the amplif ier, and V3 is obtained from one the side of the output. The current I1, coming from the microphone circuit, is defined by: I1 = GV MAM × (Equation 5) Where V M is the microphone voltage. Since the switching thre shold occurs when I1=I3, combining the above two equations yields: VM = VL × R3 R1 [] GGGG MA SARXFOHR ×× (Equation 6)

Figure 10. Basic Block Diagram For Design Purpos Since GHA is the differential gain of the hybrid amplifiers, it is divided by two to obtain the voltage V2 applied to R2.

Figure 11. Switching Threshold The “M” terms are the slopes of the li nes (0.52,0.024, and 0.0019) which are the coeffici ents of the three equations. necessary to overcome noise on the other. is connected , will affect the acoustic and side tone couplings, respectively. determine the minimum slope of that line. Using the component val ues in Equation 13 yields a G AC-MAX of –37dB. Experience has shown, however, that an acoustic coupling loss of >40dB is desirable. a minimum of 6.0dB loss is preferable. the frequency response of that level detector.

TS34118 18-20 2004/09 rev. B

Application Information

The threshold for the dial tone detector is internally set at 15mV (10mVrms) below VB (see Figure 5). That threshold can be reduced by connecting a resistor from RXI to ground. The resistor value is calculated from: R = ⎥⎦ ⎡ −1∆V V10K B Where VB is the voltage at Pin 15, and ∆V is the amount of thres hold reduction. By connecting a resistor from Vcc to RXI, the threshold can be increased. The resistor value is calculated from: R = ⎥⎦ ⎡ −− 1∆V VV10K BCC Where ∆V is the amount of threshold increase. Background Noise Monitors For testing or circuit analysis purposes, the transmit or receiv e attenuators can be set to the “on” position, by disabling the background noise monitors, and applying a signal so as to activate the level detectors. Grounding the CPR pin will disable the receive background noise monitor, thereby indica ting the “presence of speech” to the attenuator control block. Grounding CPT does the same for the transmit path. Additionally, the receive background noise monitor is automat ically disabled by the dial tone detector whenever the receive signal exceeds the detector’s threshold. Transmit / Receive Detection Priority Although the TS34118 was designed to have an idle mode such that the attenuators are halfway between their full on and full off positions, the idle mode can be biased towards t he transmit or the receive side. With this done, gaining control of the circuit from idle will be easier for that side towards which it is biased since that path will have less attenuation at idle. By connecting a resistor from C T (pin 14) to ground, the circuit will be bias ed towards the transmit side. The resistor value is calculated from: R = ⎥⎦ ⎡ −1∆V VBRT Where R is the added resistor, R T is the resistor normally bet ween pins 14 and 15 (typically 120 Ω), and ∆V is the difference between VB and the voltage at C7 at idle C refer to (Figure 10) By connecting a resistor from CT (pin 14) to Vcc, the circuit will be biased towards the transmit side. The resistor value is calculated from: R = ⎥⎦ ⎡ −− 1∆V VVR BCC T R, RT, and ∆V are the same as above. Switching time will be somewhat affected in each case due to the different voltage excursions required to get to transmit and receive from idle. For practical considerations, the ∆V shift should not exceed 100mV.

TS34118 19-20 2004/09 rev. B If a potentiometer with a standard linear taper is used for t he volume control, In sit uations where this may be objectionable, a potentiometer with an audio taper (commonly us ed in radio volume controls) will provide a more linear relationship as indicated in Figure 12. The slight non-linearit y at each end of the graph is due to the physical construction of the potentiometer, and will vary among different manufactures. Figure 12. Receive Attenuator Gain versus Potentiometer Position Using Audio Taper FI, VLC) should be considered sensitive to RFI signals.

TS34118 20-20 2004/09 rev. B SOP-28 Mechanical Drawing SOP-28 DIMENSION MILLIMETERS INCHES DIM MIN MAX MIN MAX A 17.70 18.00 0.697 0.709 B 7.41 7.59 0.292 0.299 C 10.15 10.55 0.400 0.415 D 2.37 2.63 0.093 0.104 E 1.27BSC 0.05BSC F 0.40REF 0.016REF G 0.10 0.30 0.004 0.012 H 0.60 1.00 0.024 0.040 I 0.25BSC 0.010BSC J 0.254TYP TYP K 0.5 0.020 DIP-28 Mechanical Drawing DIP-28 DIMENSION MILLIMETERS INCHES DIM MIN MAX MIN MAX A 36.95 37.21 1.455 1.465 B 13.76 14.02 0.542 0.552 C 3.81 4.06 0.15 0.160 D 0.38 -- 0.015 -- E 2.54TYP 0.100TYP F 0.45TYP 0.018TYP G 1.27TYP 0.050TYP H 0.119 0.14 3.04 0.31 J 14.986 15.49 0.59 0.61 K 0.254NOM 0.010NOM L 16.00 17.02 0.589 0.610